[CentOS] XFS : Taking the plunge

[Keith Keller]

On 2014-01-21, Steve Brooks <steveb at mcs.st-and.ac.uk> wrote:
>
>> mkfs.xfs -d su=512k,sw=14 /dev/sda
>
> where "512k" is the Stripe-unit size of the single logical device built on 
> the raid controller. "14" is from the total number of drives minus two 
> (raid 6 redundancy).

The usual advice on the XFS list is to use the defaults where possible.
But you might want to ask there to see if they have any specific advice.

> I mounted the filesystem with the default options assuming they would be 
> sensible but I now believe I should have specified the "inode64" mount 
> option to avoid all the inodes will being stuck in the first TB.
>
> The filesystem however is at 87% and does not seem to have had any 
> issues/problems.
>
>> df -h | grep raid
> /dev/sda               51T   45T  6.7T  87% /raidstor

Wow, impressive!  I know of a much smaller fs which got bit by this
issue.  What probably happened is, as a new fs, the entire first 1TB was
able to be reserved for inodes.

> Another question is could I now safely remount with the "inode64" option 
> or will this cause problems in the future? I read this below in the XFS 
> FAQ but wondered if it have been fixed (backported?) into el6.4?

I have mounted a large XFS fs that previously didn't use inode64 with
it, and it went fine.  (I did not attempt to roll back.)  You *must*
umount and remount for this option to take effect.  I do not know when
the inode64 option made it to CentOS, but it is there now.

> I also noted that "xfs_check" ran out of memory and so after some reading 
> noted that it is reccommended to use "xfs_repair -n -vv" instead as it 
> uses far less memory. One remark is so why is "xfs_check" there at all?

The XFS team is working on deprecating it.  But on a 51TB filesystem
xfs_repair will still use a lot of memory.  Using -P can help, but it'll
still use quite a bit (depending on the extent of any damage and how many
inodes, probably a bunch of other factors I don't know).

--keith



-- 
kkeller at wombat.san-francisco.ca.us