A quick and easy performance improvement

Julian Field mailscanner at ecs.soton.ac.uk
Wed Jul 26 20:18:24 IST 2006

Mike Jakubik wrote:
> Julian Field wrote:
>> I have found in the past that splitting the installation into many 
>> different partitions just causes more problems than it solves. Putting 
>> /var separate on Solaris is a classic example. People say "when your 
>> logs get big it won't fill /" which is true enough. But disks are huge 
>> and cheap these days. Why not just do it properly and roll your logs 
>> properly so they never occupy a lot of space? If you have them 
>> separate, then as you install more patches, /var/sadm will start to 
>> get very large, which there is nothing you can do about, so after 2 or 
>> 3 years your /var will fill and you'll have to start bodging things to 
>> get them out of /var to give you more room for /var/sadm.
>> I just find it causes more problems than it solves, so long as you set 
>> up your system to maintain itself properly. If you never roll 
>> /var/log/maillog on a MailScanner system then yes, it will get very 
>> large, but set it up properly and keep your logs and quarantines pruned.
> I don't think thats very true. Most systems that are setup with a single 
> / partition are done so by the clueless. Separating your partitions 
> gives you a number of advantage including protection from disk space 
> starvation, and increased performance when they are strategically laid out.
> Hard drives can transfer data much more quickly from outer tracks than 
> they can from inner tracks.  To take advantage of this you should try to 
> pack your smaller file systems and swap closer to the outer tracks, 
> follow with the larger file systems,  and end with the largest file 
> systems.

But you have absolutely no control whatsoever of the mapping from 
logical disk block number to physical location on the disk. Who's to say 
that your disk doesn't start from the inside and work outwards. You have 
*absolutely* no control nor knowledge of how this is laid out. Do they 
use a complete platter before the next one, or do they use the platters 
in turn for each disk block? You have no way of knowing or controlling 
this configuration. Pretending to know how a disk is laid out these days 
is a total fallacy.

> Separate partitions also allow different mount options, and in the event 
> of data loss due to power outages, etc, it is more likely that the 
> system will still come up, making it easier for you to restore from 
> backup as necessary.

With journalling filesystems this is totally irrelevant. They just 
replay the log (a matter of milliseconds) and come back up.

Julian Field
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