Re: Successful RAID 6 setup

[Andrew Dunn <andrew.g.dunn@gmail.com>]

Thanks for the replies.

I began using mdadm in ubuntu 8.04, which I believe was the 2.6.24
kernel. The rebuild times under this kernel with 6 500GiB drives were
very fast... I think like 100-200m, but that was with a raid5.

Using raid6 under ubuntu 9.04 , which was 2.6.28 I would get 20m rebuild
times on raid6 with 1TiB drives. This would take literally 10-14 hours
depending on my array size.

Now with ubuntu 9.10, which is 2.6.31 I get like 50-75m on the same
exact raid6 rebuild.

I didn't realize that software/OS mattered so much for performance from
kernel to kernel.

I need to look more into this bitmap that people have mentioned.


Beolach wrote:
> On Wed, Nov 4, 2009 at 11:03, Andrew Dunn <andrew.g.dunn@gmail.com> wrote:
>   
>> I sent this a couple days ago, wondering if it fell through the cracks or if I am asking the wrong questions.
>>
>> ------
>>
>> I will preface this by saying I only need about 100MB/s out of my array
>> because I access it via a gigabit crossover cable.
>>
>> I am backing up all of my information right now (~4TB) with the
>> intention of re-creating this array with a larger chunk size and
>> possibly tweaking the file system a little bit.
>>
>> My original array was a raid6 of 9 WD caviar black drives, the chunk
>> size was 64k. I use USAS-AOC-L8i controllers to address all of my drives
>> and the TLER setting on the drives is enabled for 7 seconds.
>>
>>     
> <snip mdadm -D>
>
> That array should easily be able to fill your 100MB/s speed requirement.  If
> you really are only accessing over a 1Gib/s link, I wouldn't worry much
> about tweaking for performance.
>
>   
>> I have noticed slow rebuilding time when I first created the array and
>> intermittent lockups while writing large data sets.
>>
>> Per some reading I was thinking of adjusting my chunk size to 1024k, and
>> trying to figure out the weird stuff required when creating a file system.
>>
>>     
>
> Can you quantify "slow rebuilding time"?  And was that just when you first
> created the array, or do you still see slowness when you check/repair the
> array?  Using a write-intent bitmap might help here.
>
> I don't know that any of the options discussed so far are likely to help w/
> intermittent lockups.  When you see them, are you writing your data over
> the network?  How badly does it lock up your system?  What kernel version
> are you using?
>
>
> Good Luck,
> --
> Conway S. Smith
>   

-- 
Andrew Dunn
http://agdunn.net