Premium Controllers Under Scrutiny: Ultra160 RAID Adapters from Adaptec and LSI

Comparison Of Technical Specifications

A quick look at the data sheets of the two controllers reveals a multitude of differences. The integration of the cache memory is what catches the eye at first glance. Since Adaptec solders the 32 MB ECC memory chip firmly to the circuit board, the circuit board gets by with just half the usual height (low profile). LSI, on the other hand, provides a battery buffer, in order to secure the contents of the cache memory in the event of a crash or a brownout. In addition, this controller comes with two SCSI channels instead of just one, and can therefore serve as many as 30 physical drives (up to 40 logical drives) at the same time.

Further differences can be found in the RAID modes that are supported. While both test candidates can manage 0, 1 and 5, LSI offers extended modes, focussing on data security, whereas Adaptec opts for the best possible performance. For example:

RAID 5/0 and RAID 0/5 differ in the way in which the two fundamental modes are combined. In the case of 5/0 (LSI), several RAID 5 arrays are pooled in stripesets, in order to up performance. The benefit of this is that a drive can fail in each of the RAID 5 sets without the RAID being forced to its knees. RAID 0/5 (Adaptec) requires at least three stripesets, in order to be able to compile a RAID 5. This means that the failure of as few as two drives in different stripsets would put an end to the RAID 0/5.

The disadvantage of Adaptec: a RAID 0/5 is slowed significantly by the restriction to a single Ultra160 channel. Allocation to two channels makes sense here.