SQL Server Magazine

Network Appliance's StoreVault S500 network storage appliance supports SAN and NAS and is targeted at small-to-midsized businesses (SMBs). With hot-swappable trays for up to twelve 250GB or 500GB disk drives, the system's storage capacity scales from 1TB to 6TB. Usable storage is about half or less of raw storage capacity, depending on the number of disk drives, the RAID configuration employed, and the space allocated to data snapshots. The system I tested had twelve 500GB disk drives and reported a capacity of 3343GB, including storage allocated to snapshots.

A basic StoreVault S500 system includes four 250GB disk drives and support for iSCSI and SnapRestore, NetAppís rapid file system snapshot restore software. The proprietary Write Anywhere File Layout (WAFL) file system provides emulation for both the Windows Common Internet File System (CIFS) and the UNIX/Linux file system. An optional Fibre Channel SAN interface and a SCSI interface with Network Data Management Protocol (NDMP) support for a tape backup device are also available.

Data ONTAP StoreVault Edition, NetApp's proprietary Linux-based OS, includes several fault-tolerance and performance features. Data ONTAP supports two levels of RAID: RAID 4, which dedicates one hard disk to parity information, and RAID-DP, an enhanced RAID 4 technology in which a second hard disk holds independently calculated parity information, allowing data recovery in the event of two concurrent disk failures. Because parity information isn't distributed across all the hard disks as in RAID 5 and RAID 6 configurations, administrators can add spare disks to the data array at any time and move between RAID-DP and RAID 4 configurations at will.

For added reliability, every ninth data blockó11.1 percent of raw data space—holds checksum information for the previous eight blocks. When read with the other eight blocks in a single I/O operation, the checksum provides an additional data integrity check with minuscule performance overhead. In addition to the space allocated to the checksum blocks, WAFL maintains 10 percent of the free space in the file system, trading a bit of usable storage capacity for better system performance. Interspersed with data on the disk, that 10 percent of storage capacity provides Data ONTAP with the contiguous space it needs to maintain good performance. In total, about 21 percent of raw storage capacity is allocated to these data integrity and performance features.

Data ONTAP monitors disks for signs of failure. When a spare hard disk is present, Data ONTAP can begin copying a failing disk to the spare in the background before hard failure actually occurs. By watching for signs of impending failure—an increase in the number of soft read errors, for example, or a jump in the number of reads that require two attempts before succeeding-Data ONTAP predicts an imminent failure and begins to copy the data to a spare disk drive while it still can. If hard failure occurs before that copy is complete, Data ONTAP reconstructs uncopied data by using the parity information, avoiding the performance degradation that accompanies a parity-based rebuild.

The S500 also incorporates NetApp Snapshot technology, which creates point-in-time data backups by saving a volume's metadata-the information that describes which data blocks on disk are assigned to each data file-and protecting in-use data blocks from being overwritten when files are written or updated. Using the GUI-based management interface, StoreVault Manager, administrators can configure the frequency and retention of snapshots. The S500's optional data replication feature can automatically copy the contents of a replica folder to one or more target StoreVault appliances, where it's available in read-only mode until an administrator enables read/write operations.

Installing NetApp storage appliances is typically pretty easy-this isn't the first time I've configured and tested one. (See "Network Attached Storage," May 2001, InstantDoc ID 20389, for my review of five NAS devices, including the NetApp F840.) Installing the S500 was as easy as plugging it in and connecting two network cables. You configure the appliance by using StoreVault Manager, which I installed on a workstation. StoreVault Manager is easy to navigate, with many context-sensitive menus and pop-ups, as Web Figure 1 shows. When I powered up the S500, it acquired a DHCP-assigned IP address. StoreVault Manager discovered the S500, let me log on to it, and launched a configuration wizard. The only glitch occurred when I tried to join an Active Directory (AD) domain, where the wizard hung. Instead, I configured the S500 as a workgroup member, and it came right up. Later, with the help of a NetApp technician, I corrected the problem and joined an AD domain.

I received no surprises when I tested access to Windows shares. By default the Everyone group has Full Control access, which I easily adjusted using Windows Explorer Security Properties panes. Restoring files from a snapshot is similarly easy. Snapshots retain the file system security that was present when the snapshot was taken and are stored in the snapshots folder under the top-level CIFS share, which administrators can expose (or not) using share-level permissions.

I tested the iSCSI capability in a Windows Server 2003 virtual machine after installing Microsoft iSCSI Software Initiator 2.03 and using the associated iSCSI configuration screens to connect to the S500. In StoreVault Manager, I ran the Create Lun (SAN) Wizard. After asking me to name and size the LUN, the wizard displayed the connection with the server and let me link that connection to the new LUN. After a reboot, the server's Microsoft Management Console Disk Management snap-in reported the LUN as a non-initialized disk. I initialized it and created and formatted a volume, which I then used as I would any new disk.

NetApp allocates a significant proportion of available disk space to data integrity and performance features-about 21 percent of the each disk drive allocated to data, plus one or two drives allocated to parity information. Another significant proportion of storage capacity is used by snapshots. Using storage in this way isn't altogether a bad thing, because you certainly get value in exchange for that storage space. However, you do need to adjust your expectations-only about half the raw storage capacity of your appliance might be available for file and database storage, with the balance going to snapshot .

The S500 is not an inexpensive solution, especially when compared to the cost of quality SATA disk drives these days. But when critical business operations are on the line, can you really afford to skimp? You need to answer that question yourself, but the S500 offers reliable performance with little administrative effort and promises to serve you well.

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