Re: Large cache - performance tips

Oskar Pearson wrote:

> Solaris x86 with their journalling filesystem. Put the journal on a
> disk of it's own: this will reduce open/close latencies dramatically.
> Apologies to the person (you know who you are) that I didn't believe,
> (if they are reading this.)

A jornaling file system reduces I/O wait times since the application
does not have to wait for seeks on an overloaded drive to write file
system metadata. Keeping the jornal on the same disk as hot data will
degrade the performance down to almost the same as a non-journaled file
system.

The same effect can be acheived by enabling asyncronous FS metadata
updates. Some systems like Linux use asyncronous FS updates by default,
while Solaris defaults to syncronous metadata updates.

On Solaris/SunOS you can use the unsupported "fastfs" tool to activate
asyncronous FS updates without needing to configure a jornaling
filesystem, but I'd strongly recommend using a FS jornal from crash
recovery reasons. However the fastfs method may prove slightly higher
performance due to even less I/O overhead. A fastfs:ed filesystem will
have close to the same performance carateristics as a tmpfs filesystem,
but with slightly higher persistense (surives clean shutdown or soft
crashes which syncs disks, likely to fail on powerloss).

Another good FS optimisation is to disable atime updates. This is
usually done with an FS mount option (noatime). Known to be supported on
Linux and Solaris 7 (maybe 2.6 as well, don't remeber). Quite likely
supported on a number of other OS:es as well.

--
Henrik Nordstrom
Spare time Squid hacker