xfs_growfs / planned resize / performance impact

[Eric Sandeen]

On 8/3/12 1:09 AM, Stefan Priebe - Profihost AG wrote:
> Am 03.08.2012 06:03, schrieb Eric Sandeen:
>> On 7/31/12 8:56 AM, Stefan Priebe - Profihost AG wrote:
>>> Hello list,
>>> 
>>> i'm planning to create a couple of VMs with just 30GB of space
>>> while using xfs as the main filesystem.
>>> 
>>> Now i alreay know that some of the VMs will grow up to 250GB
>>> while resizing the block device and using xfs_growfs.
>>> 
>>> Should i take care of that and format these disks with special
>>> parameters?
>>> 
>>> I've discovered that a 500GB volume has agcount=4 and 64000
>>> blocks of internal log - while a 300GB volume resized to 500GB
>>> has agcount 7 ad only 40960 blocks of internal log.
>>> 
>>> Is it a problem if this grow will happen in small portions (30GB
>>> => 50GB => 75GB => 100GB => ... 300GB)?
>> 
>> This incremental part doesn't matter a bit.  The first mkfs will
>> choose the AG count & size according to defaults; further growth
>> after this will add new (possibly partial) AGs of that pre-chosen
>> size.
> 
> OK thanks for your reply. But does this influence performance? Should
> i perhaps start creating the 30GB with agcount 1 so that while
> raising the disk i don't end up with such a high agcount value? Does
> it make sense to create a bigger internal log from he beginning?

You can't make a single-AG filesystem, for starters.

I'd really suggest that you just do some testing, and see if your
proposed mkfs/growth plan impacts your VM performance in any 
significant way.

-Eric
 
> Thanks
> 
> Stefan
>