Bill MacAllister wrote:
--On June 25, 2013 10:29:26 AM -0700 Bill MacAllister whm@stanford.edu wrote:
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.
Thanks for the followup. Modern hard drives have moved to 4096 byte physical sectors, they advertise 512 byte sectors for compatibility with older OSs. This will probably become an issue more often, although I expect modern Linux tools to be able to operate with actual 4096 byte sectors and make the issue more obvious. There should be a drive option that reports its true sector size, I just don't remember the details at the moment.