[Dovecot] XFS vs EXT4 for mail storage

[Stan Hoeppner]

On 5/2/2013 8:17 AM, Charles Marcus wrote:

> man mount doesn't show delaylog, nobarrier or noquota as valid mount
> options... ?

Many XFS mount options are kernel version specific.  Show:
~$ uname -a

Delaylog doesn't exist in recent mount(8) because it's no longer a mount
option, same goes for older mount(8).  Its existence as a mount option
didn't exist for long, WRT distro mount(8) updates.  Since 2.6.39
delaylog is the default, and as of somewhat more recently in the 3.x
tree, the old journal logging code was completely removed from the
source.  Thus there is no longer a "delaylog" mount option.  The feature
is now hard coded in XFS.

Barriers are crucial to XFS journal, and thus filesystem, reliability.
"nobarrier" isn't listed in mount(8), though "barrier" is, which is the
default mode.  Making people "look for" the switch that disables
barriers forces them to take a learning journey.  Hopefully during this
journey they become educated to the risks of disabling it, before doing
so.  "Better reliability through obscurity" you might say.  Consider the
horrible rap XFS would have today if everyone and his dog could easily
learn how to disable barriers, then did so on hardware not appropriate
for it.  Yes, exactly, corrupted XFS filesystems littering the landscape
and people screaming what a pile of dogsh|zt XFS is.

WRT noquota, it is the default.  You'd never specify it.  There are 10
quota options at the bottom of the XFS section of mount(8) that one
might want to set.

It is quite irritating, yet surprisingly common, to see XFS users
re-specifying the defaults in their /etc/fstab, because they didn't take
the time to educate themselves properly, and simply copy/pasted from one
of many online "XFS tuning guides".  On the XFS list we call these "XFS
mis-tuning guides", as nearly all of them contain mostly misinformation.
 Not intentional mind you, but because they just don't know what they're
talking about, or they did but the guide is 5+ years old, and things
have changed.

-- 
Stan