iSCSI-based storage arrays have not captured a substantial percentage of the storage market, but there are a number of compelling products out there. A healthy level of competition in this space, coupled with the relatively aggressive demeanor of the competing vendors, should give IT managers a distinct edge when shopping for new storage.
When creating your RFP (request for proposal), be sure to talk to users and developers to get a firm idea of the different storage and performance needs in the organization.
For more sample RFPs, go to go.eWEEK.com/rfp.
The following questions are designed to serve as a foundation for an RFP for iSCSI storage arrays.
What is the maximum capacity of your storage system?
List both raw and usable capacities.
• For a single storage shelf?
• At full capacity (maximum number of shelves populated with the largest-capacity drives)?
* What is the maximum throughput (in megabytes per second) supported on a single controller?
* How many controller units does the product support?
* Do you offer clustering capabilities?
Startups EqualLogic and LeftHand Networks are selling iSCSI systems that can be clustered to add storage capacity and performance.
* Does the product have redundant controllers?
* How much cache does each controller have?
List maximum value.
* Do the controllers have battery-backed cache?
The level of RAID implemented should depend on the type of application being stored.
* What levels of RAID does your product support?
Check all that apply.
• RAID 0
• RAID 10
• RAID 5
• RAID 1
• Dual-parity RAID (RAID 6)
* If your storage system does not currently support dual-parity RAID, when do you expect that such support will be added?
The issue of dual-parity RAID has risen in importance lately because of the growing popularity of SATA (Serial ATA) hard drives. SATA drives are generally less reliable than Fibre Channel and SCSI drives, and dual-parity RAID adds a level of security.
More important, however, is the issue of RAID rebuild times. SATAs high data capacity goes from being a strength to a weakness in a disk-failure scenario: Large SATA drives (with current capacities of up to 750GB each) can take hours to rebuild if a drive within a RAID dies. Dual-parity RAID adds resilience—with it, three SATA drives would have to die before data loss would occur.
* Does your array have the ability to change RAID levels non-destructively?
This ability is becoming more common, and it allows IT managers to tune their storage to changing application needs. For example, if RAID 5 turns out to be too slow, an IT manager may want to switch to a RAID 10 configuration without bringing down applications and reformatting data volumes.
* In addition to iSCSI, how does your solution connect to servers?
• Fibre Channel?
• NAS (network-attached storage)?
Many iSCSI storage systems on the market today support Fibre Channel as well as NAS. Fibre Channel is recommended for performance-intensive applications. iSCSI is much cheaper to implement and should be good enough for common applications such as e-mail.