how to get rid of bad blocks in a file on PERC 5/I?

Adam Nielsen adam.nielsen at uq.edu.au
Sat May 1 01:16:52 CDT 2010


> I suppose the argument isn't really about software vs hardware RAID
> though... if the firmware on the PERC5/I was released GPL, then the
> community can maintain and fix bugs just as well as software RAID in Linux.

Yes, I think those who dislike hardware RAID feel this way not because it's
hardware, but because the existing implementations leave a lot to be desired.
 If the firmware was GPL'd and bugs could be fixed as easily as in software
RAID then I'm sure you would find many more people moving to hardware RAID.

> Generally speaking, we've been very impressed with the PERC5/6 controllers.
> On a single controller and proper tuning with 8 drives/RAID-5, we easily
> achieve 400-500MB/sec sequential read/writes. For higher performance, we've
> used dual controllers with software RAID-1 and achieved almost double. We
> consider this a pretty cheap solution for that type of performance and the
> amount of storage space we get with the high capacity SATA drives.

My main reason for disliking hardware RAID is not the performance, but the
reliability.  As you've discovered, when something goes wrong like a dodgy
disk, it can be rather difficult to get to the bottom of what's happening.  If
the firmware was open source that sort of problem could be fixed, so really
it's the lack of control that I (and probably others) dislike.

> Although I haven't tried benchmarking an equivalent setup with software
> RAID-5, I would be curious to see what kind of performance can be achieved.
> Would using the fast CPUs we have these days for RAID-5 be faster than
> RAID-5 offloaded to a PERC5/6 controller?

I've always assumed that a CPU will be able to perform many more calculations
than a dedicated RAID controller, but I've never actually checked whether this
is the case.  At any rate you do have to share that CPU with other tasks so
it's possible that a high CPU task may slow your disks down, or lots of disk
activity will slow down your applications.  Whether this slowdown would still
result in faster performance than a hardware controller is a good question.  I
believe recent CPUs are able to perform well over 4GB/sec in RAID calculations
so I would suspect the answer is yes.  Of course the real bottleneck is the
disks, as long as the hardware RAID controller can keep up with the disks
there would be no difference in performance.

Cheers,
Adam.



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