Re: How do you calculate optimal amount of RAM required for XFS filesystems?

[Seth Mos <knuffie@xxxxxxxxx>]

At 16:53 5-12-2001 +1000, Adrian Head wrote:
> I have been lurking on this list quick some time now; but I have never seen a
> discussion regarding how to calculate the optimum amount of RAM required for
> XFS based filesystems.
>
> There was a thread a very long time ago (cannot find it now) where it was
> stated that leaps of RAM was required but didn't specify the quantity of
> heaps ;-)  For memory it also discussed the caching of filesystem data for
> performance.  But I don't think the interaction between amount of RAM and XFS
> was discussed fully.

Some of the older code needed more ram because the relied on getting it 
when it asked for it (during recovery for example).

These days 12MB is a minimum requirement to boot a XFS box and perform 
recovery as well.

If you have more then this you just start caching data and everything feels 
faster.
If you have a webserver you could use 256 MB or more to make sure that the 
speed stays up by caching a lot of the static data. If your working static 
working set is about 1 GB of data, 512 MB ram should be able to cache a lot 
of the requests. Also take into account that certain programs run a _lot_ 
faster when they can also fit in memory.

> Does anyone have experience on this subject?
>
> Say - how much RAM is required for a 80G or 120G XFS file system?

32MB would work just fine and more is better.

> Does having many different sized XFS partitions change anything?

No. Well some small things might add up, but I think you don't see that 
untill the TB range.

> For example I have 1x 40G, 1x80G, 1x120G XFS partitions on the same
> fileserver with 384M RAM.  Is this enough?

If people are reading _and_ writing this data at random over all the disks 
then it is more then enough. If there is more data read then written, 
buying more ram is a sane thing to do.
If this is for a internet server behind a 64Kbit line that won't help the 
people leeching from it :-)

A politically correct answer would be "it depends".

Cheers

--
Seth
Every program has two purposes one for which
it was written and another for which it wasn't
I use the last kind.