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Re: High load times with mdb

--On June 25, 2013 10:29:26 AM -0700 Bill MacAllister <whm@stanford.edu>

> With the release of Debian 7 (wheezy) I was rebuilding a couple test
> systems and was surprised to find that the load times I am seeing for
> populating the mdb database with slapd have gone up dramatically.  The
> load for a master server that was taking about 10 minutes just took
> 35 minutes.  The slave is worse.  A normal load time is 20 minutes
> and it is at 31 minutes now with an eta of about 2.5 hours. 

I tested this file system and that file system with this set of options and
that set of options and really never moved the problem significantly.  I
finally realized I should believe my experiments and think about what else
could be causing the problem I was seeing.

What changed about the same time that I starting building with
wheezy/stable was that I removed a partition option that had been added to
improve performance on our VM farm, i.e. align-at:4k.  Our LDAP servers are
physical servers after all.  Reinstating the parameter resulted in
dramatically faster, and reproducible, load times on any file system I
tried.  We are now using ext4 for our LDAP server farm, well, we are when I
get done rebuilding them.

This problem will be specific to the disk in use.  Looking at the
manufacturers documentation it never really states what the block size it,
but implies it is 512 bytes.  I think that is a lie, I am told most modern
disks lie about their geometry.  In any case, for the disks we are using 4k
alignment works.

Thanks everyone for the suggestions.



Bill MacAllister
Infrastructure Delivery Group, Stanford University