Re: raid5 software vs hardware: parity calculations?

[Robin Bowes <robin-lists@robinbowes.com>]

Bill Davidsen wrote:
> Robin Bowes wrote:
>> Bill Davidsen wrote:
>>  
>>> There have been several recent threads on the list regarding software
>>> RAID-5 performance. The reference might be updated to reflect the poor
>>> write performance of RAID-5 until/unless significant tuning is done.
>>> Read that as tuning obscure parameters and throwing a lot of memory into
>>> stripe cache. The reasons for hardware RAID should include "performance
>>> of RAID-5 writes is usually much better than software RAID-5 with
>>> default tuning.
>>>     
>>
>> Could you point me at a source of documentation describing how to
>> perform such tuning?
>>   
> No. There has been a lot of discussion of this topic on this list, and a
> trip through the archives of the last 60 days or so will let you pull
> out a number of tuning tips which allow very good performance. My
> concern was writing large blocks of data, 1MB per write, to RAID-5, and
> didn't involve the overhead of small blocks at all, that leads through
> other code and behavior.

Actually Bill, I'm running RAID6 (my mistake for not mentioning it
explicitly before) - I found some material relating to RAID5 but nothing
on RAID6.

Are the concepts similar, or is RAID6 a different beast altogether?

>> Specifically, I have 8x500GB WD STAT drives on a Supermicro PCI-X 8-port
>> SATA card configured as a single RAID6 array (~3TB available space)
>>   
> No hot spare(s)?

I'm running RAID6 instead of RAID5+1 - I've had a couple of instances
where a drive has failed in a RAID5+1 array and a second has failed
during the rebuild after the hot-spare had kicked in.

R.