[Gllug] OT: Replace old model WD Raptor with new within CentOS

[general_email at technicalbloke.com]

gvim wrote:
> On 25/05/2010 07:42, t.clarke wrote:
>   
>> I recall that the controller in use is an LSI MegaRaid, in which case I would
>> imagine that the only people that could give you a definitive answer are the
>> tech support guys at LSI.   I have used them in the past - they are helpful -
>> and LSI have a toll-free number from the UK  (check their website).
>>
>>     
>
> LSI UK said that as long as the new disk's size and spindle speed is the same everything should be OK. Now I'm confused :-( as LSI are contradicting Western Digital.
>
> gvim
>
>   


I struggle to see why it shouldn't be. I can see how putting a slower
drive in would give you a problem but the new drive has slightly better
seek. Also I could see how a drive from a different series or
manufacturer with a different internal geometry or number of platters
might affect performance but it sound like the drive in question is a
pretty minor revision. Does anyone know if the number of blocks per
internal cylinder ever gets changed mid series? That could give you
severe performance problems but it seems unlikely to me they would
change such a thing.

Surely there's got to be some natural variation in seek times between
supposedly identical drives anyway, RAIDs cope with that OK. Also when
one drive in a RAID remaps a bad sector it creates an asymetry which
will cause that block to read and write slower than it's siblings. That
must happen fairly often and raid controllers seem to cope alright.

Having said I'm no expert on servers & RAID. It's an intriguing question
and it would be good for everyone to have an answer. Dare I suggest it's
time to try it? You can always flog it on ebay as nearly new if it does
cause performance problems - if it doesn't work you're going to need to
spend a packet on new disks anyway, what's £20 depreciation out of >£500 eh!

Roger.
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