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Re: Admin Guide: Tuning 21.1.2 Disks and virtual servers

Guillaume Rousse wrote:
> Le 11/01/2010 18:08, Gavin Henry a écrit :
>>> So, let's say I'm crazy and I want to investigate putting ldap servers
>>> on VMware Guests --- do I care about any of the directions in section
>>> 21.1.2 about separating the logs and the db or not?

>> Yes, that still applies for best performance.
> I may be wrong, but write to DB logs only apply when changes occurs in 
> the directory. So the gain for separating logs and data file are mostly 
> sensible if you have lots of changes. And without exact numbers, it's 
> hard to say if is really worth, especially on fask disk with large 
> throughput.

Basically true. But you should realize that a lot of things that one would
normally expect to be read-only operations may actually be read-write. For
example, if you're authenticating to a server that logs authentication
successes and failures.

Ultimately, whether the app layer is virtualized or not, multiple spindles at
the physical layer is a win. If all of the filesystems in your VM are mapped
onto a single disk in the host, your performance is going to be swamped by all
the seek overhead, and that's true regardless of whether it's read or write
traffic. (Possible exception: for readonly traffic on an SSD, the seek
overhead is pretty small. Still measurable, but compared to rotating disc
media, it's negligible.)

Any sysadmin worthy of the title ought to understand that. This is not
specific to OpenLDAP administration, this is the way computer systems work.
The VM case doesn't bear highlighting in the OpenLDAP docs.
  -- Howard Chu
  CTO, Symas Corp.           http://www.symas.com
  Director, Highland Sun     http://highlandsun.com/hyc/
  Chief Architect, OpenLDAP  http://www.openldap.org/project/