[Dovecot] XFS vs EXT4 for mail storage

[Stan Hoeppner]

On 5/2/2013 8:21 AM, Reindl Harald wrote:
> 
> 
> Am 02.05.2013 15:17, schrieb Charles Marcus:
>> but what I'm still unsure of for a VM
>> environment is the delaylog and nobarrier options.

Delaylog is fine for VM guests.  The barrier settings may all simply be
useless because many hypervisors don't pass barriers down the stack from
the guest.  Which means things like fdatasync don't work, not just
journal write barriers.  See:

http://xfs.org/index.php/XFS_FAQ#Q:_Which_settings_are_best_with_virtualization_like_VMware.2C_XEN.2C_qemu.3F

This has negatively affected EXT4 on ESXi, not just XFS.

>> Are these recommended/optimal for a VM? Running on ESXi (does it matter what hypervisor ie being used)?
> 
> barriers does not help you much or are implicit because you
> have no physical disk under the FS and the underlying storage
> should have battery backed buffers and doe snot need to confirm
> the physical write to the disk to have the data safe

The problem isn't lack of a physical disk under the guest.  The problem
is lack of software support in the hypervisors.  I don't have an answer
as to which versions of ESXi/vSphere/etc, if any, do or do not support
write barriers, fdatasync, etc.  I'm not finding it in their
knowledgebase, though I've not put much effort into it yet.  You'll need
to do some research.

-- 
Stan