raid-5 to raid-10 conversion for PERC-6i?

Alexander Dupuy alex.dupuy at mac.com
Tue Feb 16 12:35:26 CST 2010


I wrote:
>> The only approach that I can see might be to remove a drive from the 
>> RAID-5 (making it into a RAID-0), 

Stroller replied:
> Removing a drive from a RAID5 does not make it a RAID0 - it makes it a 
> degraded RAID5, BTW.
It depends on how you do the removal.  Using the MegaCli command-line 
tool, if you do a logical drive reconstruction to remove the drive from 
RAID-5, you will end up with a RAID-0, e.g.:

MegaCli -LDRecon -Start -R0 -Rmv [E32:S3] -L1 -a0

This capability is also possible with the Web/BIOS under the 
Reconstruction Wizard.

Marking the drive offline or missing, will of course give you a degraded 
RAID-5.

> I'm a little confused why you want to do this, and all this way. You 
> seem to be acting penurious about drives, ... perhaps this is simply 
> related to the number of drives you can fit in your RAID cage at one 
> time?

PowerEdge 1950 with four 2.5" drive bays - although I also have some 
2950 systems, which have eight bays (five occupied), allowing more 
flexibility - on one of those systems, I could add three drives, 
allowing a full RAID-10 to be created by the spares (3 new + 1 taken 
from the RAID-5).  It would probably be easier on those systems to move 
the contents of the RAID-5 to the two disk RAID-0 that takes up the 
other slots.

> I've read recently (here?) that RAID10 &/or RAID01 performs better 
> than RAID5, but RAID5 is really nice & flexible & easily expandable - 
> surely if performance was a major bottleneck & consideration, you 
> would have planned for this? I'm not putting you down, but most of us 
> don't need to bleed every ounce of performance from our hardware.

The answer: it depends.  For (random and/or small) writes, a RAID-10 
will have better performance than RAID-5; for reads, the RAID-5 (with 
the same number of drives) will be better.  So the performance benefit 
will depend on the read/write mix, which can change depending on 
workload (and thus is not always possible to plan for).   There's a nice 
blog series that shows this at 
http://kendalvandyke..com/2009/02/disk-performance-hands-on-series.html

> I would imagine that migrating a RAID0 or RAID1 to RAID10 or RAID01 
> might well be officially supported

RAID-0 to RAID-1 is supported, but there seems to be no way to convert 
even these into RAID-10.

@alex

-- 
mailto:alex.dupuy at mac.com



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