[LARTC] Swap size

[LARTC] Swap size

[wlagmay]

Hi All,

This is out of the topic question, but I'm hoping that you can help me. If for
example I'm going to install a Fedora 4 64-bit with 8 to 12 Gig of physical
memory, how much swap file of directory do I need to create?

Thank you very much,

Wennie

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Re: [LARTC] Swap size

[lartc]

hi wennie,


On Mon, 2006-03-20 at 10:44 +0300, wlagmay@yanbulink.net wrote:
> Hi All,
> 
> This is out of the topic question, 
yep.

> but I'm hoping that you can help me. If for
> example I'm going to install a Fedora 4 64-bit with 8 to 12 Gig of physical
> memory, how much swap file of directory do I need to create?
red hat suggests 3x physical memory, therefore, 24 to 36 gigs of swap.

you have a lot of memory.

cheers

charles


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Re: [LARTC] Swap size

[Kajetan Staszkiewicz]

Dnia poniedzia³ek, 20 marca 2006 08:44, wlagmay@yanbulink.net napisa³(a): 

> Hi All,
>
> This is out of the topic question, but I'm hoping that you can help me. If
> for example I'm going to install a Fedora 4 64-bit with 8 to 12 Gig of
> physical memory, how much swap file of directory do I need to create?

Do you really need any swapspace? Are you sure you will have enough programs 
running to eat all the memory you have?

-- 
| pozdrawiam / greetings | powered by Trustix, Gentoo and FreeBSD |
|  Kajetan Staszkiewicz  | jabber,email: vegeta () tuxpowered net |
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Re: [LARTC] Swap size

[gypsy]

wlagmay@yanbulink.net wrote:
> 
> Hi All,
> 
> This is out of the topic question, but I'm hoping that you can help me. If for
> example I'm going to install a Fedora 4 64-bit with 8 to 12 Gig of physical
> memory, how much swap file of directory do I need to create?
> 
> Thank you very much,
> 
> Wennie

Wennie,

You seem to think that the amount of physical RAM should have something
to do with the amount of swap space.  If so, that is wrong.

Even with huge, and 8 gigs of RAM is huge, amounts of RAM, you need a
dedicated swap partition.  Don't believe those who say you don't.

The size of the swap partition should be at least 512 megs.  The maximum
should normally be no more than 2 gigs.  I like to spread this out over
4 disks.  My setup creates a partition on each of the 4 hard drives in
my system and then /etc/fstab has an entry for each partition that says
/dev/hd#	swap	swap	defaults,pri=1	0	0
--
gypsy
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Re: [LARTC] Swap size

[William L. Thomson Jr.]

Off Topic

I am not a swap fan these days. I am not to sure it's really that
necessary. If the system has adequate memory for the applications and
task it will be doing. Most times there will be little to no swap used
ever. The more memory, the less likely you will ever swap. And if you do
it's very small amounts.

Any way you look at it swapping is bad. You are substituting one of the
slowest components for one of the fastest. Either way swapping kills
performance. Sure it could be the difference of out of memory, and apps,
machine crashing, halting etc. Rare. Most times it's a hit in
performance not needed.

Those rules of thumb for swap size vs ram size is only relevant if you
have small amounts of ram. A system these days needs a min of 512,
either physical or combo, swap and physical. Once you top 512MB of
physical memory. Your needs for swap start diminishing. 1GB or more of
ram, and hardly the need for any swap. At that point I tend to use
256-512Mb just to be safe. However I have seen years go by on some
servers, with little to no swapping. So I max out on most machines at
256MB swap these days.

IMHO swapping is bad. If you are swapping more than a 10-20MBs, more
than likely you are best off to get some more ram. Unless that's not an
option then maybe another machine. When you do swap, things slow down,
so I just seen no reason in it.

Granted it was needed for the low mem systems of yester year. These days
you can get a 512MB-1GB stick of ram for $50 or so. Hardly relevant any
more. I have been toying around with getting rid of swap all together in
some of my machines. When I experimented on a core NAS server. Only
times I would have issues, was every now and then during heavy Gentoo
updated/compiling. But not always, and never show stoppers.

But the jury is still out for no swap here.

-- 
Sincerely,
William L. Thomson Jr.
Obsidian-Studios, Inc.
http://www.obsidian-studios.com

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Re: [LARTC] Swap size

[lartc]

hi all,

woops forgot -- that whole thing about maximum swap partition size :-/

yikes -- 

still a ton of memory  :-)

cya

charles
-- 
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have you believe ... a superlative oxymoron" --anonymous


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Re: [LARTC] Swap size

[Peter Surda]

gypsy wrote:
> Even with huge, and 8 gigs of RAM is huge, amounts of RAM, you need a
> dedicated swap partition.  Don't believe those who say you don't.
On the contrary. I run many systems without any swap at all.

What you get by using swap is (from a very simplified point of view) 
that if you use up all memory, instead of the programs crashing, the 
system gets "slower" (but keeps running). Whether to use swap or not 
depends on what you're doing with your computer.

> gypsy
Yours sincerely,
Peter

-- 
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Re: [LARTC] Swap size

[Carl-Daniel Hailfinger]

gypsy schrieb:
> The size of the swap partition should be at least 512 megs.  The maximum
> should normally be no more than 2 gigs.

IIRC the 2 GB limit for swap partitions on i386 was lifted a few years ago.

Regards,
Carl-Daniel
-- 
http://www.hailfinger.org/
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Re: [LARTC] Swap size

[Carlos Blanquer]

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On 3/20/06, Peter Surda <surda@shurdix.com> wrote:
>
> gypsy wrote:
> > Even with huge, and 8 gigs of RAM is huge, amounts of RAM, you need a
> > dedicated swap partition.  Don't believe those who say you don't.
> On the contrary. I run many systems without any swap at all.
>
> What you get by using swap is (from a very simplified point of view)
> that if you use up all memory, instead of the programs crashing, the
> system gets "slower" (but keeps running). Whether to use swap or not
> depends on what you're doing with your computer.


I disagree in the point that you necessary needs swap. With that amount of
RAM, it's not needed making any swap of any size. I don't think it'll use
all of these.
By the way, there are some ways to use all that RAM so I suggest to put 512
MB of swap o 1 Gig, no more.
This is by the fact that, if in anytime the systems gets out of RAM,
swapping some low prio proceses will decide wich threads must stop without
sacrifying any important data.




--
Atentamente,
              Carlos.
-------------------------------
LTIM Member - http://ltim.uib.es
BkP Staff (Servidores, Gamer Area, Tesorean) -
http://www.balearikus-party.org

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Re: [LARTC] Swap size

[wlagmay]

Thanks to all, but to be more particular, Im going to use the machine with 8 or
12 Gig of physical memory for squid caching, and we all know that caching
consumes to much memory. Our objective actually is to cache the most popular
pages on the memory so that it will be faster to access by the clients.

so far there are 3 ideas, 1st no swap dir at all, 2nd physical memory multiply
by 2 or 3 and the 3rd one creating a swap with 512 MB  to 1 Gig. On my
scenario, wherein im going to use the system for caching, which one is more
applicable?


Thanks,

Wennie

Quoting Carlos Blanquer <relayito@gmail.com>:

> On 3/20/06, Peter Surda <surda@shurdix.com> wrote:
> >
> > gypsy wrote:
> > > Even with huge, and 8 gigs of RAM is huge, amounts of RAM, you need a
> > > dedicated swap partition.  Don't believe those who say you don't.
> > On the contrary. I run many systems without any swap at all.
> >
> > What you get by using swap is (from a very simplified point of view)
> > that if you use up all memory, instead of the programs crashing, the
> > system gets "slower" (but keeps running). Whether to use swap or not
> > depends on what you're doing with your computer.
>
>
> I disagree in the point that you necessary needs swap. With that amount of
> RAM, it's not needed making any swap of any size. I don't think it'll use
> all of these.
> By the way, there are some ways to use all that RAM so I suggest to put 512
> MB of swap o 1 Gig, no more.
> This is by the fact that, if in anytime the systems gets out of RAM,
> swapping some low prio proceses will decide wich threads must stop without
> sacrifying any important data.
>
>
>
>
> --
> Atentamente,
>               Carlos.
> -------------------------------
> LTIM Member - http://ltim.uib.es
> BkP Staff (Servidores, Gamer Area, Tesorean) -
> http://www.balearikus-party.org
>




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Re: [LARTC] Swap size

[Jason Boxman]

wlagmay@yanbulink.net said:
>
> Thanks to all, but to be more particular, Im going to use the machine with 8
> or
> 12 Gig of physical memory for squid caching, and we all know that caching
> consumes to much memory. Our objective actually is to cache the most popular
> pages on the memory so that it will be faster to access by the clients.
>
> so far there are 3 ideas, 1st no swap dir at all, 2nd physical memory
> multiply
> by 2 or 3 and the 3rd one creating a swap with 512 MB  to 1 Gig. On my
> scenario, wherein im going to use the system for caching, which one is more
> applicable?

First, always use swap.  The only common reason to choose not to use swap
under Linux is on a workstation where the user believes VM pressure is
causing unwanted latency for interactive operations.  This scenario is
easily resolvable with tunable nobs for the Linux 2.6 VM and its entirely
unnecessary to avoid creating a swap partition.

As you've discovered, with 12GB of RAM using a 2 or 3 multiply rule is
hardly reasonable.

Ideally you will pick a value based on testing your workload against the
actual machine in question.  Personally, I rarely allocate more than 4GB of
swap and never less than 512M with today's large disks.  If you're worried
about performance, you can stripe swap over multiple disks or disk arrays. 
Granted, you should never heavily be in swap, but if the circumstance arises
it allows you to recover in some fashion.  It's the difference between a
dead machine and a recoverable one.

These days, I'd suggest a multiplier of simply 1, 0.5, or 0.25 for creating
swap.

Or did you _really_ need that 4-12GB of disk space for something more
important than increased stability and availability of the machine in
question? (If the answer is _yes_, buy _more_ disk.)



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Re: [LARTC] Swap size

[Carlos Blanquer]

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On 3/21/06, wlagmay@yanbulink.net <wlagmay@yanbulink.net> wrote:
>
>
> Thanks to all, but to be more particular, Im going to use the machine with
> 8 or
> 12 Gig of physical memory for squid caching, and we all know that caching
> consumes to much memory. Our objective actually is to cache the most
> popular
> pages on the memory so that it will be faster to access by the clients.


I haven't used Squid, but I thought  that Squid uses Hard Disk space to
caching.
Maybe you can use RAM, but in Squid config you must specify what quantity of
hard disk memory and how much time it can store the cached info.


so far there are 3 ideas, 1st no swap dir at all, 2nd physical memory
> multiply
> by 2 or 3 and the 3rd one creating a swap with 512 MB  to 1 Gig. On my
> scenario, wherein im going to use the system for caching, which one is
> more
> applicable?


I think 1 Gig is sufficient. Relaying on the fact that you'll use your hard
drive to caché all the squid info.

Anyway, 1 Gig is the right option in my view.




--
Atentamente,
              Carlos.
-------------------------------
LTIM Member - http://ltim.uib.es
BkP Staff (Servidores, Gamer Area, Tesorean) -
http://www.balearikus-party.org

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Re: [LARTC] Swap size

[Carlos Blanquer]

[-- Attachment #1.1: Type: text/plain, Size: 782 bytes --]

On 3/21/06, Jason Boxman <jasonb@edseek.com> wrote:
>
> wlagmay@yanbulink.net said:
>
>
> As you've discovered, with 12GB of RAM using a 2 or 3 multiply rule is
> hardly reasonable.


Sorry?
That's a 36 GB swap ( 12 x 3 )?
So much memory at all.

Ideally you will pick a value based on testing your workload against the
> actual machine in question.  Personally, I rarely allocate more than 4GB
> of
> swap and never less than 512M with today's large disks.  If you're worried
> about performance, you can stripe swap over multiple disks or disk arrays.


That's right.

--
Atentamente,
              Carlos.
-------------------------------
LTIM Member - http://ltim.uib.es
BkP Staff (Servidores, Gamer Area, Tesorean) -
http://www.balearikus-party.org

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Re: [LARTC] Swap size

[Anton Glinkov]

If the machine will be used only for squid, I suggest you create no more
than 1GB of swap, just in case the physical memory runs out. You can play
with the cache_mem setting in squid.conf and see what is the maximum value
with which it doesn't use swap-space (after all what you seek is cache
speed).

>
> Thanks to all, but to be more particular, Im going to use the machine with
> 8 or
> 12 Gig of physical memory for squid caching, and we all know that caching
> consumes to much memory. Our objective actually is to cache the most
> popular
> pages on the memory so that it will be faster to access by the clients.
>
> so far there are 3 ideas, 1st no swap dir at all, 2nd physical memory
> multiply
> by 2 or 3 and the 3rd one creating a swap with 512 MB  to 1 Gig. On my
> scenario, wherein im going to use the system for caching, which one is
> more
> applicable?
>
>
> Thanks,
>
> Wennie
>
> Quoting Carlos Blanquer <relayito@gmail.com>:
>
>> On 3/20/06, Peter Surda <surda@shurdix.com> wrote:
>> >
>> > gypsy wrote:
>> > > Even with huge, and 8 gigs of RAM is huge, amounts of RAM, you need
>> a
>> > > dedicated swap partition.  Don't believe those who say you don't.
>> > On the contrary. I run many systems without any swap at all.
>> >
>> > What you get by using swap is (from a very simplified point of view)
>> > that if you use up all memory, instead of the programs crashing, the
>> > system gets "slower" (but keeps running). Whether to use swap or not
>> > depends on what you're doing with your computer.
>>
>>
>> I disagree in the point that you necessary needs swap. With that amount
>> of
>> RAM, it's not needed making any swap of any size. I don't think it'll
>> use
>> all of these.
>> By the way, there are some ways to use all that RAM so I suggest to put
>> 512
>> MB of swap o 1 Gig, no more.
>> This is by the fact that, if in anytime the systems gets out of RAM,
>> swapping some low prio proceses will decide wich threads must stop
>> without
>> sacrifying any important data.
>>
>>
>>
>>
>> --
>> Atentamente,
>>               Carlos.
>> -------------------------------
>> LTIM Member - http://ltim.uib.es
>> BkP Staff (Servidores, Gamer Area, Tesorean) -
>> http://www.balearikus-party.org
>>
>
>
>
>
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>


-- 
Anton Glinkov
network administrator

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Re: [LARTC] Swap size

[Tomas Simonaitis]

I agree, 1-2GB of swap is good choice from my experience.
I don't think you should run without swap at all - there usually is something 
OS can push to swap and free some ram.

On Wednesday 22 March 2006 17:56, Anton Glinkov wrote:
> If the machine will be used only for squid, I suggest you create no more
> than 1GB of swap, just in case the physical memory runs out. You can play
> with the cache_mem setting in squid.conf and see what is the maximum value
> with which it doesn't use swap-space (after all what you seek is cache
> speed).
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Re: [LARTC] Swap size

[William L. Thomson Jr.]

On Wed, 2006-03-22 at 19:19 +0200, Tomas Simonaitis wrote:
> I agree, 1-2GB of swap is good choice from my experience.
> I don't think you should run without swap at all - there usually is something 
> OS can push to swap and free some ram.

Well it can't hurt in the sense that it's not like hard drive space is
limited these days. Or unused swapping causing any harm.

However if you start swapping more than 128MB or 256MB it's more than
likely going to be noticeable. More so for the intended application and
goal.

Thus it might be a good idea to have 512MB-1GB of swap. But as soon as
you see >50MB or swap being used, or any noticeable use of swap. You
will want to either get more ram, or make software adjustments. IMHO

-- 
Sincerely,
William L. Thomson Jr.
Obsidian-Studios, Inc.
http://www.obsidian-studios.com

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Re: [LARTC] Swap size

[Brett]

wlagmay@yanbulink.net wrote:
> 
> Hi All,
> 
> This is out of the topic question, but I'm hoping that you can help me. If for
> example I'm going to install a Fedora 4 64-bit with 8 to 12 Gig of physical
> memory, how much swap file of directory do I need to create?
> 

Many people on this thread are giving information which they believe to 
be true, but in most cases it isn't (having the right mix of RAM/swap, 
and having data swapped to disk, can make your computer *more* 
responsive). If you want accurate information you should visit the 
kernel mailing list and/or read the kernel source / docs). There is a 
large amount of information available on how to tune your kernel swap 
variables.

The same advice goes for squid (and how squid can best use RAM (eg: you 
*won't* make squid perform better by assigning it large amounts of RAM 
directly). There is a large amount of posts on the squid-users mailing 
list regarding swap and memory use.

HTH
Brett
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