Re: recommended way to add ssd cache to mdraid array

[Thomas Fjellstrom <thomas@fjellstrom.ca>]

On Fri Jan 11, 2013, Stan Hoeppner wrote:
> On 1/11/2013 6:20 AM, Thomas Fjellstrom wrote:
> > On Thu Jan 10, 2013, Chris Murphy wrote:
> >> Another thing to look at is if you're using XFS, what your mount options
> >> are. Invariably with an array of this size you need to be mounting with
> >> the inode64 option.
> > 
> > I'm not sure, but I think that's the default.
> 
> No, inode32 has always been the default allocator.  It was decided just
> recently to make inode64 the default, and the patcheset for this was
> committed on 9/20/2012, ~3 months ago, into 3.6-rc1-17:

Ahh. I somewhat sorta try and keep up to date on kernel happenings, and after 
a while things get muddled. So that's probably where I got that from.

> http://oss.sgi.com/archives/xfs/2012-09/msg00397.html
> 
> So with 3.6+ kernels inode64 is the new default.  Any current mainstream
> distro kernel defaults to inode32.
> 
> Worth noting:  if you upgrade the kernel on a system with existing
> inode32 XFS filesystems the allocator for these will remain inode32
> unless the mount option is manually changed.  This is the same behavior
> as with current kernels.  New filesystems created after upgrading to a
> 64 bit kernel w/this patch set will be mounted with inode64.  IIRC 32
> bit kernels are limited to the inode32 allocator and 32 bit inodes.
> 
> There are many workloads that prefer, or even require, 32bit inodes,
> and/or the behavior available with the inode32 allocator.  Thus it would
> not be smart to auto convert them to inode64 after a kernel upgrade.


-- 
Thomas Fjellstrom
thomas@fjellstrom.ca