RAID 0+1 using 10000rpm and 7200rpm HDD?

[Chris Drake]

Hi Thorsten,

I'd guess that the cache installed on each drive will also have an
effect, as will the kind of data you're working with (I'm guessing you
have a good reason for the 10Krpm drives), so I doubt any theoretical
reply is going to match the "real" answer, which would only be
obtained from testing various scenarios - do let us know how the tests
turn out if you choose this path.

BTW - I noticed recently (using IBM's excellent "DFT" - drive fitness
test - disk, that identical looking drives with identical model
numbers can have different sized RAM caches on them) - and of course
that DFT tells you what the installed cache on each drive really is :-)

Kind Regards,
Chris Drake

Monday, May 17, 2004, 10:01:27 PM, you wrote:

TJ> Hi

>> RAID 0 (on Intel IHC5-R)
>> Western Digital Raptor 74GB 10000rpm SATA
>> Western Digital Raptor 74GB 10000rpm SATA
>> 
>> RAID 0 (on Promise FastTrak 378)
>> Seagate Barracuda 7200.7 120GB 7200rpm SATA
>> Seagate Barracuda 7200.7 120GB 7200rpm SATA
>> 
>> I would like to create a RAID 0+1 from this config but I wonder if I'm
>> about to loose on performances doing the RAID 1 between the two (2) RAID 0
>> volumes since the first volume has 10000rpm HDD and the second one has
>> 7200rpm HDD.
>> 
>> What do you think?

TJ> Read performance will be as fast as the 10000 rpm raid can read. Write 
TJ> performance will go down to the write performance of the 7200 rpm raid (or 
TJ> even slightly lower).
TJ> But this is only a generall answer as it depends on the speed of the 
TJ> individual harddisks. The 7200 rpm disk with higher capacity _may_ be as 
TJ> fast as the 10K rpm disk with lower capacity because the 120GB disk can
TJ> read more data per rotation (depending on the geometry of the disk).
TJ> 10000 rpm is a 38% speed increase over 7200 rpm, 120 GB is a 67% capacity 
TJ> increase over 72 GB. A portion of these 67% will go to more tracks/disk, 
TJ> but
TJ> it _may_ happen that the 120 GB disks are as fast as the 10K 72 GB disks.

TJ> Maybe its worth playing around with the disks to get the ideal 
TJ> performance.

TJ> Viele Grüsse,
TJ> Thorsten