[RndTbl] RAID5 rebuild performance

Adam Thompson athompso at athompso.net
Fri May 20 17:08:05 CDT 2011

In any event, yes, a single U320 bus can only do 320MB in aggregate, and its practical limit is around 80% of that.  HP's external enclosures are not exactly notorious for being well-balanced equipment...
Only one model in any given product generation will be a single-bus design, that's the economy model.
On a Sun E450 with Ultra-II (40MB/sec) drives, the system backplane is engineered so that no more than 4 drives are connected to any one channel, for example.
Generally speaking, the 4-disk per channel limit is sound engineering.
There's also a curious effect that I've seen but can't explain where more spindles actually slows down the array drastically... I suspect if you recreate that array as RAID 50, you'd see performance gains.

Trevor Cordes <trevor at tecnopolis.ca> wrote:

>On 2011-05-20 Kevin McGregor wrote:
>> When the SCSI controller BIOS is initialized, it lists all of the
>> drives on both channels, and most of them (as I recall) are described
>> as being set to 80 MB/s with a note that the OS will probably set
>Weird, see if the SCSI BIOS setup screens let you manually select the
>SCSI speed.  You might have to drill down to the per-drive area.  I
>know my U320 card gives me choices.
>80MB/s per drive isn't shabby, though your drives can probably push
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