IBM System Storage DS3512 Express review

Network storage arrays aimed at SMBs are invariably offered with only SATA hard disks to keep costs down. IBM's latest System Storage DS3500 family brings 6Gbits/sec SAS within their grasp, and here we put the DS3512 through its paces and see whether compromises have been made in the search for value.

The DS3500 family consists of two head unit options, with the DS3512 on review supporting 12 3.5in drives. The DS3524 is also a 2U appliance, but can handle up to 24 2.5in disks; prices for this start at £3,087. Both models have a single controller that can be upgraded with a second where they run in active/active mode.

IBM gets the value ball rolling: along with standard SAS and full disk encryption (FDE) SAS drives, it also offers near-line SAS. These new drives deliver the high capacity and low cost of SATA but with SAS drive electronics. Offered with 7.2k spindle speeds, they do away with the need for a SATA-SAS interposer, so reducing manufacturing costs and potential failures. They also have the same level of host queueing support as standard SAS drives.

The DS3500 controllers offer plenty of connection options. You start with a pair of fixed 6Gbits/sec SAS ports for DAS applications, but there's room for a daughtercard, and IBM offers dual-port 6Gbits/sec SAS or quad-port 8Gbits/sec Fibre Channel and Gigabit iSCSI options. Our review system came with the 8Gbits/sec Fibre Channel card.

Expansion potential is based on the drive count, not the number of shelves. Each controller has an embedded 36-port SAS expander linked to its expansion port, so a pair can support up to 96 hard disks. You can daisy-chain as many shelves as you like, as long as you don't go over this number of drives.

You can mix and match IBM's EXP3512 and EXP3524 expansion shelves, join them with multiple redundant SAS paths and have different SAS drive types within the same shelf. The controllers have 1GB of cache, but the battery backup plays a different role to what it usually does. In the event of a power failure it keeps the controller running, so cache contents can be de-staged to an on-board 8GB SD memory card.