[Gllug] Re: RAID on laptop or xfs?

[Christian Smith]

On Sat, 2 Apr 2005, Martin A. Brooks wrote:

>Bruce Richardson wrote:
>
>>Oh, certainly.  But I'd rather have either of them running on SCSI than
>>IDE.  The point in this thread has been the unreliability of IDE, not
>>journalling.
>>
>>
>
>Which, to my knowledge, has been mythical for several years, at least 7
>or 8.
>
>I used to know a chap who worked for Western Digital. He told me that
>only difference between IDE and SCSI drives manufactured by WD was
>interface electronics and warranty hence the price difference.


WD is proabbly an exception, as they're the only ones who produce 10K RPM
IDE drives. Most manufacturuers who make IDE and SCSI drives have disjoint
mechanical drive specifications. SCSI drives tend to be smaller, as 10 36G
drives will perform better than a single 360G drive. SCSI drives also
often have smaller platters and more powerful voice coil head actuators,
to cut random access time and latency.

As Bruce said, cache and control is on the controller board.

Where SCSI gets it right in this regard, and IDE may be catching up, is
tagged command queueing. This way, the SCSI drive can reorder writes to
optimize performance, but will only notify the successful write when it is
done, without holding up the initiation of further writes. The OS can use
the tagged commands to implement correct ordering.

Christian

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