Re: potentially lost largeish raid5 array..

[David Brown <david@westcontrol.com>]

On 24/09/2011 14:17, Stan Hoeppner wrote:
> On 9/23/2011 7:11 PM, Thomas Fjellstrom wrote:
>> On September 23, 2011, Stan Hoeppner wrote:
>
>>> When properly configured XFS will achieve near spindle throughput.
>>> Recent versions of mkfs.xfs read the mdraid configuration and configure
>>> the filesystem automatically for sw, swidth, number of allocation
>>> groups, etc. Thus you should get max performance out of the gate.
>>
>> What happens when you add a drive and reshape? Is it enough just to
>> tweak the
>> mount options?
>
> When you change the number of effective spindles with a reshape, and
> thus the stripe width and stripe size, you definitely should add the
> appropriate XFS mount options and values to reflect this. Performance
> will be less than optimal if you don't.
>
> If you use a linear concat under XFS you never have to worry about the
> above situation. It has many other advantages over a striped array and
> better performance for many workloads, especially multi user general
> file serving and maildir storage--workloads with lots of concurrent IO.
> If you 'need' maximum single stream performance for large files, a
> striped array is obviously better. Most applications however don't need
> large single stream performance.
>

If you use a linear concatenation of drives for XFS, is it not correct 
that you want one allocation group per drive (or per raid set, if you 
are concatenating a bunch of raid sets)?  If you then add another drive 
or raid set, can you grow XFS with another allocation group?

mvh.,

David