Point 9: An Overview of Network Attached Storage

Network Attached Storage (NAS) devices contain built-in operating systems and software optimized to meet data storage requirements. NAS devices use filers as file servers in Local Area Networks (LANs) to manage data storage.

This ReferencePoint provides an overview of NAS and explains the installation, configuration, analysis, and tuning of filers. In addition, it shows how to manage the backup and recovery of NAS.

Introducing NAS

NAS devices are storage devices that are connected to a network directly and shared by multiple end users. The features and benefits of NAS devices are:

• Platform Independence: NAS devices can be deployed on client-server networks running on multiple operating systems. This is possible because NAS devices have different communication channels for different operating systems. For example, these devices communicate with UNIX environments using Network File System (NFS) and with Microsoft Windows environments using Common Internet File System (CIFS).

• Plug-and-Play Support: NAS devices can be disconnected from or connected to a network at any time without disrupting network performance.

• Task Specificity: NAS devices perform specific tasks, such as Web caching, audio-video streaming, tape backup, and data storage.

Platform Independence with NFS and CIFS

Platform independence in NAS is implemented with NFS and CIFS. For example, in the network shown in Figure 7-1-1, NFS and CIFS shares have been created on UNIX and Windows NT server. UNIX clients access the NAS device volume using the NFS mount on the UNIX server and Windows NT clients access the NAS device volume using the CIFS mount on the Windows NT server.

Figure 7-1-1: NFS and CIFS Mounting of NAS Device Volumes

Comparison of SAN and NAS

Table 7-1-1 lists the differences between NAS and Storage Area Network (SAN) technologies:

Table 7-1-1: Comparison of SAN and NAS

Feature	Implementation in SAN	Implementation in NAS
Network connectivity	Uses fiber-channel cables	Uses Ethernet cables
Hardware required to transfer data over a network	Uses routers, bridges, and gateways	Does not require additional hardware
Practical usage	Provides large volumes of storage space for data	Provides faster access to data

NAS is a network-centric technology that speeds up data access in a network. Due to the availability of a dedicated NAS device for file I/O in a LAN, clients can access data directly without using a LAN server. Figure 7-1-2 shows a LAN to which a NAS device is connected:

Figure 7-1-2: A NAS Device on a Local Area Network

NAS devices use gigabit Ethernet cables to connect to the network. Gigabit Ethernet cables and support a large number of clients over a single Network Interface Card (NIC). Some NAS devices also support multiple NICs, which enables multiple networks to use a single NAS device.

SAN is a data-centric technology that consists of multiple storage devices and includes components to manage storage devices. SAN devices can be connected by high-speed fiber channel cables for faster performance. Figure 7-1-3 shows how a SAN can be connected to a LAN:

Figure 7-1-3: Connecting a SAN to a LAN

Introduction to Filers

Filers are NAS devices that work as dedicated file servers. The advantages of using filers are:

• Reduced Network Load: Most LANs consist of a general-purpose server that provides file, print, database, and login services to clients. These servers often slow down when CPU-intensive data processing operations are done. By using a filer as a file storage service, you can reduce the load on general-purpose servers.

• Platform-independence: Filers support NFS to store data from UNIX environments and CIFS to store data from Microsoft Windows environments. As a result, it is possible to share data on filers across different operating system platforms.

• Easy Administration: Filers consist of embedded software tools to perform data management, data protection, client access support, and administrative tasks. These tools provide simple and easy-to-use Graphical User Interfaces (GUIs) for administrative tasks.

Figure 7-1-4 shows a filer network:

Figure 7-1-4: A Filer Network

Functions of Filer Software

Filers use a built-in operating system to coordinate data storage and manage the filer hardware. For example, the NetApp filer consists of the Data ONTAP operating system. The filer operating system provides utilities and tools to administer a filer, and replicate and secure data on a filer.

Administering a Filer

The filer operating system includes a remote administration tool that provides an easy-to-use GUI to administer the filer. The administration tool eliminates the need to learn programming languages or command-line interfaces to configure and maintain filers. You can access the Web-based GUI and navigate the screens to perform tasks that would have otherwise required the use of a programming language.

The administration tool helps install the filer software easily. After assigning an IP address to the filer from a console or a Dynamic Host Configuration Protocol (DHCP) server, you can use the setup wizard to configure the filer quickly.

Replicating Filer Data

The filer operating system includes replication software to mirror data on multiple network filers. The replication software continually updates the mirrored data to keep it current and available for recovery. Replication software performs three types of mirroring:

• Incremental Mirroring: Replicates a subset of the entire filer data and reduces network bandwidth requirements. First time replication transfers the entire data on the source filer volume to the destination filer. Subsequent replications perform incremental updates only with new and changed data blocks replicated on the destination filer.

• Checkpoint Mirroring: Creates checkpoints during data transfers using replication software. If the target or source filer is unavailable, transfer restarts from the most recent checkpoint.

• Cascade Mirroring: Replicates data over distant geographical locations. A target mirror filer is a source for other filers, with each mirror pair running on its own schedule to meet site-specific requirements. A high-cost link replicates data across distant locations and lower-cost links replicate across close locations.

Securing Data on Filers

The security features supported by the filer operating system are:

• Managing Data on Multiple Servers: The filer data security software can manage data stored on the UNIX and Windows platforms. Take an example of a network consisting of ten UNIX and five Windows servers. In this type of network, each server has to manage data stored locally on the server storage. These servers require additional hardware investment and administrative costs. It is possible to plug a single filer into these networks, and create logical NFS and CIFS storage partitions, which map to physical partitions on multiple computers, on the filer.

• Support for Resource Partitioning: Creates separate logical storage partitions on a filer for different end users on a network. As shown in Figure 7-1-5, a logical storage partition can use partitions created across different computers. Logical storage partitions created on a filer also support authentication services.

  
  Figure 7-1-5: A Filer Network

Installing Filers

You need to configure filer hardware and software to enable them to communicate with the network. This is done using an installation mechanism that connects to the filer from a remote administration console, invokes the filer configuration wizard, and specifies the filer hardware and software settings.

This section describes the installation and configuration of the Sun StorEdge 8600 Filer. Before you install the filer, ensure that it is connected to the administration console. The administration console can be on any Unix- or Windows-based computer.

To connect to a filer from a UNIX-based console, log on to the console as root and type tip –9600 /dev/ttya at the UNIX prompt.

To connect to a filer from a Windows-based console:

1. Select Start->Run. The Run dialog box appears.

2. Type hypertrm and click OK. The Connection Description dialog box appears, as shown in Figure 7-1-6:

   
   Figure 7-1-6: The Connection Description Dialog Box

3. In the Connection Description dialog box, specify an arbitrary name for the connection between the console and the filer and select a connection icon.

4. Click OK. The Connect To dialog box appears, as shown in Figure 7-1-7:

   
   Figure 7-1-7: The Connect To Dialog Box

5. In the Connect To dialog box, select the COM port to connect to the filer from the Connect using list.

6. Click OK. The COM1 Properties dialog box appears.

7. Specify values for the different options in the COM1 dialog box, as shown in Figure 7-1-8, and click OK.

   
   Figure 7-1-8: The COM1 Properties Dialog Box

After establishing a connection with the administration console, the filer displays the Command window. In the Command window, press ENTER. At the OK prompt, type boot to start the 8600 Filer Configuration wizard.

In the Filer Configuration wizard, specify the values for all options as listed in Table 7-1-2:

Table 7-1-2: Options of the Filer Configuration Wizard

Option	Value
Choose a language	0
Choose a locale	0
Choose a terminal type	3 or 12
Do you have network connectivity?	Yes
Is DHCP used?	No
Select the primary network interface	Hme0
Type the host name	Specify the name of the filer
Type the IP address	Specify the IP address assigned for the filer
Is IPv6 used?	No
Confirm the above information	Yes
Is Kerberos security used?	No
Confirm the above information	Yes
Name the service	Specify the service to authenticate the filer connection
The domain name	Specify the domain name assigned for the filer
The domain server IP address	Specify the domain IP address assigned for the filer
Confirm the name service information	Yes
Is the system part of a subnet?	Yes
Type the netmask	Specify the subnet mask to connect to the 8600 filer
Confirm the time	Specify the region, time zone, date, and time to set the time of the filer; this time schedules backup and restore operations
Type and verify the root password	Specify the root password to connect to the filer

After you specify values in the Filer Configuration wizard, the 8600 filer system reboots and configures the filer.

Administering and Configuring Filers

Filers provide a Web-based administration tool to administer and configure filers. The tool can be invoked from any computer on the filer network by using a Web browser. The Web-based administration tool is used to:

• Configure the permissions of end users and groups who access data stored on a filer.

• Specify a list of network host computers that can access data stored on a filer.

• Create network shares for filer directories.

• Configure the NIC of a filer.

• Configure the services, such as e-mail notification and domain naming service (DNS), provided by a filer.

Sun StorEdge 8600 filers provide the Sun StorEdge N8000 administration tool. To start the N8000 Filer administration tool:

1. Start Internet Explorer and type http://hostname:8080 in the URL field, where hostname refers to the name of the filer.

2. Press ENTER. The Password dialog box appears.

3. Type the password specified during filer installation and click OK. The N8000 Filer administration tool is invoked, shown in Figure 7-1-9:

   
   Figure 7-1-9: The N8000 Filer Administration Tool

The N8000 Filer administration tool consists of six panes: Users, Groups, Hosts, Shares, Network, and Settings.

Users Pane

The Users pane provides the Login, Primary Group, and Array fields to configure permissions for user accounts for the administration tool. The Users pane is used to specify the login name for an end user. The Primary Group field specifies the name of the group to which the end user belongs and the Array name allocates a particular disk array to an end user in multi-array filer environments.

The Users list to the left of the Users pane in the Filer administration tool interface displays a list of all end users who can access the data on the filer. When you right-click a user name, a shortcut menu appears. Table 7-1-3 lists the options of the shortcut menu:

Table 7-1-3: Options in the Shortcut Menu of the Users List

Menu Option	Purpose
View User	Displays the details of an end user in the Users pane of the Filer administration tool
Add User	Activates all the fields in the Users pane
Change User	Changes the values in the Primary Group and Comment fields
Remove User	Deletes the selected user account from the filer

Note

The Remove User option does not delete an end user’s home directory. This directory can be deleted only by using the filer operating system commands.

Groups Pane

When you select the Groups tab, the Groups list replaces the Users list. When you right-click a group name, a shortcut menu appears, as shown in Figure 7-1-10:

Figure 7-1-10: The Sun StorEdge N8000 Filer Administration Tool

Table 7-1-4 lists the functions of each option in the shortcut menu:

Table 7-1-4: Options in the Shortcut Menu of the Groups List

Menu Option	Purpose
View Group	Displays the name of a group and the end users belonging to that group in the Groups pane of the Filer Administration tool. Click the Members button to view a list of all end users belonging to a group.
Add Group	Activates the Group field in which you specify the name of the new group to be created and enables you to add end users to a group.
Change Group	Changes the members of a group.
Remove Group	Removes a group account from the filer.

Hosts Pane

A host is a computer on the network to which the filer is connected. Each host has a unique IP address, a computer name, and a number of alias names. Figure 7-1-11 shows the N8000 Filer Administration tool with the Hosts pane active:

Figure 7-1-11: The Hosts Pane of the Sun StorEdge N8000 Filer Administration Tool

Table 7-1-5 lists the options in the shortcut menu displayed in Figure 7-1-11:

Table 7-1-5: Options in the Shortcut Menu of the Hosts List

Menu Option	Purpose
View Host	Displays the host name, IP address, and alias names of the selected host. You need to click the Aliases button to view the list of alias names assigned to a particular host.
Add Host	Activates the Hostname, IP Address, and Aliases fields of the Hosts pane. Specify the details of the new host to be added and click Update to affect the changes.
Remove Host	Deletes the selected host account from the filer.

Shares Pane

Shares are specific directories on a filer accessible to other network hosts and their end users. Each shared directory has a unique name. The Shares list displays a list of share names present on a filer. To configure shares on a filer, you need to use the Shares pane. Figure 7-1-12 shows the N8000 Filer Administration tool with the Shares pane active:

Figure 7-1-12: The Shares Pane of the Sun StorEdge N8000 Filer Administration Tool

When you right-click a share name, a shortcut menu appears, which has the following options:

• Add Share: Creates a share on a particular directory

• Change Share: Changes the permissions assigned to an existing share

• Remove Share: Deletes the selected share from the filer

  Note

  Deleting a share does not delete the directory related to that share.

Table 7-1-6 lists the fields in the Shares pane of the Filer Administration tool:

Table 7-1-6: Fields in the Shares Pane of the N8000 Filer Administration Tool

Field	Description
Array	The name of the filer disk array that contains the shared directory.
Directory	The directory on the filer being shared.
Description	The name of the share that appears in the Share list.
Ownership	The login name of the owner of the shared directory. Only the owner of a directory has the right to set share permissions on the directory. By default, the root user is the owner of a directory.
Global Access	The access level that hosts on the filer network have on the shared directory. There are two types of access levels, read-only and read/write.
Host Access	The level of access level that hosts on the filer network have on the shared directory. When you click Assign Access, the Host Access dialog box appears, which is used to assign access levels to specific hosts.

Network Pane

The Network pane configures the NICs installed on the filer. When you install the filer, you specify the interface name, IP address, and subnet mask of the primary network interface. Use the Network pane to set up additional network interfaces for a filer.

The Network list, which appears to the left of the Network pane, displays the names of all network interfaces installed on a filer. Figure 7-1-13 illustrates the Network pane:

Figure 7-1-13: The Network Pane of the Sun StorEdge N8000 Filer Administration Tool

When you right-click any of the interface names, a shortcut menu appears. Table 7-1-7 lists the options in the shortcut menu:

Table 7-1-7: Options in the Shortcut Menu of the Network Pane

Menu Option	Description
View	Displays the details of the selected network interface. For an interface that is not configured, the IP address field is set to 0.0.0.0.
Change	Activates the Hostname, IP Address, and Subnet Mask fields. This option changes the hostname, IP address, and mask address of a selected interface.
Disable	Resets the selected network interface to an unconfigured state.

Note

Do not confuse the hostname specified in the Network pane with that specified in the Hosts pane. In the Network pane, hostname is the unique name associated with a network interface.

Settings Pane

The Settings pane has three options:

• Email Notification: Specifies a list of all e-mail addresses to which an e-mail message has to be sent when hardware fails in any of the filer disk arrays. To enable the EMail Notification option, use the Hosts pane of the Filer Administration tool to create a host related to the network mail server.

• NIS: Changes the Network Information Service domain to which the filer belongs. The Network Information Service domain distributes data files across multiple hosts.

• DNS: Changes the Domain Name Service settings stored on a filer. The filer uses the DNS settings to identify the IP address of a host based on the host name.

Figure 7-1-14 shows the Sun StorEdge N8000 Filer Administration tool with the Settings pane active:

Figure 7-1-14: The Settings Pane of the Sun StorEdge N8000 Filer Administration Tool

Analyzing and Tuning Filer Performance

Analyzing the performance of a filer helps detect problems associated with the filer hardware and software. Monitor the performance of filer disk arrays using one of three tools: SNMP notification, syslog error reporting, and array command line interface (CLI).

SNMP Notification

When an event, such as a disk failure that requires attention, occurs in the filer disk array, the filer operating system sends an SNMP Trap to the SNMP Manager. The SNMP Manager receives the SNMP trap and notifies the administrator about the event.

Tip

You can install SNMP Manager software on any computer in a filer network.

An SNMP trap is a User Datagram Protocol (UDP) packet, which consists of an event description, a header that identifies the type of the event, and the IP address of the host computer. UDP converts data messages generated by computer hardware into data packets.

Syslog Error Reporting

The disk array controller of the filer has a syslog utility. The utility is activated automatically when you switch the filer on. The syslog utility executes as a daemon thread in the background. The utility reports four types of messages:

• Error: Indicates a critical system event, such as an over-temperature condition, which requires immediate attention.

• Warning: Indicates a system event that is important but not urgent, such as a disabled disk array on which a recovery procedure is being executed.

• Notice: Indicates a system event, such as a power switch in the off position, which can be a result of other events or a normal condition.

• Information: Indicates a system event that has no effect on the health of the system. An example of this message is a report on the healthy state of a disk array.

The syslog utility sends these messages to an administrator host that records the messages in a syslog database.

Array Command Line Interface

The performance of disk arrays can also be monitored by using commands such as vol, sys, and fru. To run these commands, connect to the filer using a telnet session from the administration console and log on as root. A telnet session between the filer disk array and the administration console is an array CLI.

Tuning the Performance of a Filer

Performance tuning is the combined task of measuring performance, identifying bottlenecks, and altering configuration settings to fine-tune a NAS device. Perform the activities listed in Table 7-1-8 to enhance the performance of a filer. Different filers provide different management tools to perform each of these activities:

Table 7-1-8: Performance Tuning Activities

Activity	Description
Measuring performance	Measures the performance of different hardware components of a filer using measurement tools, such as Network Appliance CIFSBench and IntelIometer. Performs clean measurements when the filer is free from I/O activities and baseline measurements before starting production on a NAS device.
Enforcing disk quotas	Partitions the space available on a filer across end users and sets limitations on disk usage for end users by using tools such as the Sun StorEdge Filer Administration Tool and NetApp MultiStore software.
Enabling filing policies	Specifies the types of files stored on the filer and block unwanted file types, such as games and cartoons.
Performing self-cleanup	Generates and sends reports to different end users of a filer notifying end users of their disk usage statistics and installing disk cleanup tools using tools, such as the NetApp DataFabric Manager. The Windows Disk Cleanup utility cleans up space on a filer volume by mounting it as a CIFS volume on the Windows system.

NAS Backup and Recovery

Backing up and restoring business data is crucial for round-the-clock data availability. Some technologies to backup and restore data are snapshots, server-to-server mirroring, NFS/CIFS, and NDMP.

Snapshots

Snapshots are similar to shortcuts of files in the Windows environment and give a static view of the filesystem as it existed at the time of backup.

You can schedule snapshot backup operations for a folder stored on a NAS device by accessing the folder from a Windows or UNIX host and using the host-based volume manager utility. Figure 7-1-15 shows the snapshots taken for a folder, MyProject, on an hourly and daily basis:

Figure 7-1-15: Snapshots of a Folder Taken at Different Times

As shown in Figure 7-1-15, the MyProject folder consists of three files. The daily.0, hourly.0, and hourly.1 folders contain a copy of the MyProject folder taken at different times.

Server-to-Server Mirroring

In snapshots, backup copies of data are stored on the same NAS device as the source data. Server-to-Server mirroring creates a replica of the data stored on one NAS device on another NAS device.

As shown in Figure 7-1-16, the server-to-server mirroring technique, replicates data stored on multiple small filers to a super filer across a LAN or Wide Area Network (WAN) connection:

Figure 7-1-16: The Server-to-Server Mirroring Technique

The disadvantage of the snapshot technique is that the backup copies are lost when the source data is lost. Server-to-Server mirroring overcomes this disadvantage by storing the source and backup data at different locations. In addition, if the super backup filer is located in a different location, instantaneous recovery can be done in case of disasters at the source location.

NFS/CIFS

Server-to-Server mirroring maintains two copies of data, one on the super filer and another on the tape library. This technique consumes a lot of storage space. The NFS/CIFS backup technique involves mounting volumes on the NAS device as NFS/CIFS shares and using these shares to back up the data. The NFS/CIFS mounts point to the source data and do not contain a separate copy of the data.

As shown in Figure 7-1-17, you can mount a volume on the NAS device as an NFS volume on to a UNIX machine or a CIFS volume on to a Windows machine. You can use a UNIX or Windows backup utility, such as dump and NTBACKUP, to back up the volume on the NAS device using the NFS/CIFS share.

Figure 7-1-17: The NFS/CIFS Backup Technique

Some of the disadvantages of the NFS/CIFS backup technique are:

• Impact on Performance: NAS devices give lower priority to backup processes, such as NDMP backups and the dump and NetBackup commands issued directly to a NAS device volume. If the NFS/CIFS mount technique is used, the NAS device cannot distinguish between file requests for the backup process and file requests for other end user processes. As a result, backup processes are given the same priority as other end user processes. Backup processes consume a lot of cache memory and normal file requests are devoid of cache memory services.

• Loss of CIFS ACL: If an NFS mount backs up a NAS device volume, the Windows-based Access Control List (ACL) information of the volume is lost.

• Loss of Unicode File Names: NFS does not support Unicode file-naming conventions. For example, a volume on a NAS device contains files created using Windows NT and named in Unicode format. When this volume is backed up using an NFS mount, the original file name is replaced with a NFS-friendly name in the backup copy. NFS-friendly names are different from the original file names.

• Loss of New Technology File System (NTFS) Alternate Data Streams: In NTFS volumes, a file consists of multiple streams of data that store the ACL information, file data, and format settings. When NTFS volumes are backed up using NFS mount, the data streams do not translate to the actual data, resulting in data loss.

NDMP

NDMP defines standards to control the backup and recovery of data stored on a NAS device. To back up and recover data on a NAS device using NDMP, the operating system of the NAS device needs to include support for NDMP. The third-party utility used to perform the backup operation needs to include support for NDMP.

Figure 7-1-18 shows the components performing backup operations using NDMP:

Figure 7-1-18: The NDMP Backup Technique

Table 7-1-9 lists the components performing backup and restore operations using NDMP:

Table 7-1-9: Components of an NDMP Backup and Restore Operation

Component	Description
NDMP Server Application	A daemon application included within the operating system of a NAS device. Switch the NAS device on to invoke the application.
DMA	A Data Management Application that provides the end user interface to perform the NDMP backup operation.
Primary Storage System	The system that contains the source data to be backed up.
Secondary Storage System	The system that contains the backup device to which the data has to be backed up.
Control Connection	A TCP/IP data connection between the primary storage system and the secondary storage system.
Data Service	An NDMP service that transfers data from the primary storage to the data connection.
Tape Service	An NDMP service that transfers data from a data connection to a tape library.
SCSI Service	An NDMP service that transfers data from a data connection to a Small Computer System Interface (SCSI) device.

Depending on the secondary storage system, NDMP backup operations are classified as filer-to-filer if the secondary storage system is a filer and filer-to-server if the secondary storage system is a UNIX or Windows-based server.

One of the disadvantages of the NDMP backup technique is that NDMP backups are not portable. Different vendors of NAS devices implement the NDMP server application differently. As a result, the format in which the NDMP server application sends backup data to the DMA differs.

During restoration, the DMA needs to send data to the NDMP application in the same format as during the backup. As a result, the data backed up from a NetApp filer cannot be restored on to a Sun StorEdge 8600 filer because the NDMP server application of NetApp and Sun StorEdge filers use different data formats.

Backing Up and Restoring Filer Data

Backup and restore software included with the filer operating system can be used to make a back up or recover data quickly and efficiently. Filer backup and restore software use the snapshot technology to perform backup and restore operations. This enables efficient use of storage by storing block-level changes between each successive snapshot. The snapshot process is automatic and instantaneous, resulting in significantly faster backups.

Managing NAS

A network administrator needs to be familiar with the daily management activities performed on NAS devices. When managing NAS devices, you need to monitor the performance of these devices, troubleshoot hardware and software problems, and migrate data from distributed local storage to a NAS device.

Monitoring the Performance of NAS Devices

NAS devices provide counters to monitor the performance of the CPU, memory, network, and file system of NAS devices. Table 7-1-10 lists some of the frequently used counters:

Table 7-1-10: NAS Device Performance Counters

Counter	Description
CPU Utilization	The time for which the CPU is busy with handling file I/O, incoming client requests, outgoing replies, and Redundant Array of Inexpensive Drives (RAID) management.
Network Interface Statistics	The set of counters that specify the amount of data received and transmitted over a network by the NAS device, the information about NIC buffer overflow, and the number of Ethernet collisions.
Disk Utilization	The time for which the disk head has been busy performing read/write operations. This data helps to identify the over utilized disks.

Some of the applications built into NAS devices to monitor system performance are Network Appliance DataFabric Manager, EMC Control Center Symmetrix Manager, and Multi Router Traffic Grapher (MRTG).

Network Appliance DataFabric Manager

Network Appliance DataFabric Manager is a remote management utility built into NetApp cache appliances and filers. This software is used to:

• Monitor the usage and availability of disks and hot drives.

• Monitor system settings, such as temperature, power supplies, and fan performance.

• Monitor the utilization of protocols, such as HTTP, FTP, NNTP, NFS, and CIFS.

• Measure the number of bytes and packets read or written over the network, and the errors associated with each network interface.

• Send an e-mail or pager notification to an administrator on detecting hardware or software problems.

• Provide graphs and reports to help analyze system performance based on past and current data.

EMC Control Center Symmetrix Manager

EMC Control Center Symmetrix Manager is a management utility built into EMC Symmetrix storage systems. This software monitors the performance of channel and disk directors and generates physical and logical views of NAS device hardware configurations.

Multi Router Traffic Grapher

Multi Router Traffic Grapher (MRTG) is a general-purpose network traffic management utility used with NAS devices from any vendor. This utility reads the traffic counters of a NAS device network connection from a router and creates detailed graphs showing the status of the monitored network connection. The graphs are created as HTML pages and can be viewed using a Web browser.

Troubleshooting Hardware and Software Problems

NAS device vendors provide Field Replaceable Units (FRUs) for hardware liable to pose problems. For example, most NAS vendors provide one or two hot disk drives. When one of the disks in the NAS disk drive array fails, the data on the damaged disk is copied to the spare disk and all read/write operations are performed from the spare disk. In addition, most vendors provide multiple Ethernet channels to a single NIC. When one channel links fails, alternate links automatically perform data transfer.

Tip

The NAS device management software sends a notification to the administrator about the link and disk failures. In case of failures in other hardware components, such as the CPU, the motherboard, and the power supply, it is best to let an experienced technician fix the error.

Software errors that occur on a NAS device can be classified into three categories: system bugs, system panics, and system hangs.

System Bugs

System bugs are errors that are part of the NAS operating system software and cannot be fixed by an end user. The bugs in the NAS operating system can be fixed by purchasing upgrade software or patches from the NAS device vendor.

System Panics

System panics are errors that can occur when the NAS operating system code performs an illegal operation, such as a function trying to read disk blocks with illegal block numbers. System panics cause the NAS device to shut down, reboot, and dump memory contents to a file, core file. You need to send the core file to the NAS device vendor and get the error fixed.

System Hangs

System hangs are errors that occur in a NAS device due to the watchdog mechanism. The watchdog mechanism performs a coordinated check between the hardware and software of the NAS device. After a predefined time, the operating system of the device increments a counter in the memory.

The Read Only Memory Basic Input/Output System (ROM BIOS) firmware periodically checks to see if the counter has been incremented. If the counter has not been incremented, the BIOS firmware assumes that the NAS device operating system is not functioning and reboots the system.

Migrating Data from a Local Storage to a NAS Device

Copying data across platforms involves the migration of data across different filesystems, such as UNIX File Systems (UFS) and NTFS. Commonly available softwares built into NAS devices to perform data migration are:

• NDMPcopy: Transfers data between two NAS devices across a dedicated network connection using the NDMP protocol. The NDMPcopy software supports full and incremental copies of data to be transferred and supports volume- or directory-level copy operations.

• Network Appliance SnapMirror: Mirrors data across two or more filers. This software is built into NetApp filers and supports incremental, checkpoint, and cascade mirroring. It does not need additional resources to manage the replication process.

• EMC Celerra TimeFinder/FS: Migrates complete volumes from one Symmetrix NAS device to another. This software enables volumes to be mirrored across remote sites and supports splitting of mirror volumes.

• cp, xcopy, and tar Commands: Copy data from UNIX- and Windows-based computers to NAS devices. The UNIX cp and Windows xcopy commands copy UFS and NTFS volumes on to a NAS device volume.

• Remote Tape Utility: Copies data from a remote tape to a NAS device. This utility is provided by UNIX-based NAS device vendors.

  Note

  The NDMPcopy, SnapMirror, and TimeFinder software can migrate UFS and NTFS volumes across NAS devices.

When migrating data across NAS devices, ensure that the software you use to perform the migration provides support for migration of metadata and access control lists (ACL). For example, the xcopy command copies ACLs along with data when migrating NTFS volumes to a NAS device. In addition, ensure that soft links, which are symbolic links to directories on other volumes, are also migrated. The cp command follows symbolic links and copies the target of the links to the destination location.