choosing a file system

[Adam Tauno Williams]

> > I had the feeling whatever optimizations done at the FS level would give
> > us a max of 5-10% benefit.
> > We migrated from ext3 to reiserfs  on our cyrus servers with 30k
> > mailboxes. I am not sure I saw a great benefit in terms of the iowait.
> > At peak times I always see a iowait of 40-60%
> To be honest, that's not what we saw in our ext3 <-> reiserfs tests.
> What mount options are you using? Are you using the mount options I 
> mentioned?
> noatime,nodiratime,notail,data=ordered

FYI, noatime implies nodiratime.  You can set nodiratime without atime,
but not atime without nodiratime.

> > But the new Solid-State-Disks seem very promising. They are claimed to
> > give 30x the throughput of a 15k rpm disk. If IO improves by 30 times
> > that should make all these optimizations unnecessary.
> > As my boss used to tell me ... Good hardware always compensates for
> > not-so-good software.
> What we've found is that the meta-data (eg mailbox.db, seen db's, quota 
> files, cyrus.* files) use WAY more IO than the email data, but only use 
> 1/20th the space.

Ditto.  The meta-data is very much the hot-spot for I/O.

> By separating the meta data onto RAID1 10k/15k RPM drives, and the email 
> data onto RAID5/6 7.2k RPM drives, you can get a good balance of 
> space/speed.

Agree.