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swap questions

swap questions

If one does not have the time to identify individual swapping needs on 70 servers, would a swap size equal to memory in addition to pseudo-swapping be a safe (smart) bet even if memory sizes were sometimes 8 and 16 gig?

Thanks in advance
7 REPLIES
MANOJ SRIVASTAVA
Honored Contributor

Re: swap questions

Hi Dan

Anyhting between 1-2 times the swap is a good place to start with .


Manoj Srivastava
Tracey
Trusted Contributor

Re: swap questions

I've always heard/done 2x's the memory. It has worked well so far.
A. Clay Stephenson
Acclaimed Contributor

Re: swap questions

Hi Dan,

I tend to be a radical in this but I very seldom adopt the old 2x-3x rule. In fact, I typically enable only 256-512MB of primary
swap with pseudo-swap enabled.

The whole reason I bought the memory was so that I wouldn't swap in the first place! Using 2x-3x (which is 4x-6x with mirrors) for disk that I will never use is dumb. If you want to feel safe in machines with large amounts of RAM then (here I go being radical again) enable file system swap at very low priority. It will almost certainly never be used but if it is you then have the swap and it is allocated dynamically.

I do suggest in these cases that you set up a separate dump area at 1x RAM plus a bit more
and don't mirror it.

The only time I use the old 2x-3x rule is in systems with very little memory.

My 2 cents, Clay
If it ain't broke, I can fix that.

Re: swap questions

Clay,

When you suggest using fs swap, is that for the primary swap? And if this is so, then why do you need to set the priority low?

Re: swap questions

Sorry to bother again...Is the percentage of RAM that pseudo swap uses a tunable perameter?
A. Clay Stephenson
Acclaimed Contributor

Re: swap questions

Hi Dan,

No you have no control over then percantage of RAM for swap. Pseudo-swap is 0 or 1 (off or on). You must have some primary swap space, 256 MB is about minimum and it has priority 1. fs swap can then be assigned priority 3 or so.
That way, primary swap is completely used before filesystem swap is touched.
If it ain't broke, I can fix that.
Manju Kampli
Trusted Contributor

Re: swap questions

if you are concerned about the disk space, and you are sure the system does not use too much of swap frequently, then psudo swap is the best way. If system starts using swap, the system performance will die (when compared to dedicated swap)

If you have less memory, then allocating the dedicated swap is good.

using File system swap is good when you are not sure how much swap is required for the system and you don't want to dedicate the disk space only for swap.

hope this helps,
manju
Never stop "LEARNING"