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

Bond Masuda bond.masuda at jlbond.com
Fri Apr 30 11:24:40 CDT 2010


Hi Tim, Adam

Thanks for responding. Remarks inline below...

> In the case of a RAID controller, standard practise is for the
> controller to reconstruct the data from the other drives, and then
> issue
> the write instruction back to the original drive.  The better RAID
> implementations will actually REPORT THIS TO YOU, when it happens (e.g.
> Linux software RAID, so that you know the drive may be unwell).  To
> make
> matters worse you can't even reliably check the SMART data yourself
> with
> some of the Dell/LSI controllers - and LSI/Dell don't seem to care
> enough to fix this...
> 
> https://bugzilla.kernel.org/show_bug.cgi?id=14831
 
With smartmontools 5.39.1, i was able to get the SMART stats off the drives
through the PERC5/I:

smartctl -A -d megaraid,X /dev/sdc, where X={0,1,...,7}

> Using smartctl to check what's gone on the with the drive itself would
> be the best thing to do, I think...  Recent smartctl has support for
> communicating with drives behind PERCs.

indeed we did. most of the SMART data was normal except on 1:6 which showed

attribute#200 Multi_Zone_Error_Rate was 277 (all other drives it was 0)

> ACK.  My conclusion is also to use AHCI, and software RAID.  It's more
> reliable generally, and if you do find a bug, the maintainers are
> responsive (or you can even fix it yourself, or pay someone else to -
> this is Open Source right?  Presumably that's why people use Linux in
> the first place?).  Oh, and it's cheaper too.

i have nothing against software RAID, we chose hardware RAID since it
essentially came with the PowerEdge server and we figured given it was
available there would be an advantage of using hardware RAID in RAID-5.

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.

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.

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?

-Bond





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