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#1 (**permalink**) 01-18-2008, 08:11 AM

Hello --

As part of a sweeping system performance upgrade, I plan on migrating
the contents of my single system disk onto two 740GD Raptors, slaved
together as RAID0. Question: where do I put the swap partition?
Obviously, partitioning a RAID array doesn't help performance one
jot, so how do I get around this?

Thanks for any help,

Rohan Beckles
rohan.beckles@virgin.net
--
1x ASUS PC-DL Deluxe
2x Intel Xeon "Prestonia" @ 3.06GHz
1x Corsair TwinX2048-3200C2 (2x1GB)
1x Seagate Barracuda II 20GB
1x ABIT Siluro Ti4200-8x AGP 128MB DOTH OTES

#2 (**permalink**) 01-18-2008, 08:11 AM

Rohan Beckles <rohan.beckles@virgin.net> wrote:
> As part of a sweeping system performance upgrade, I plan on migrating
> the contents of my single system disk onto two 740GD Raptors, slaved
> together as RAID0. Question: where do I put the swap partition?
> Obviously, partitioning a RAID array doesn't help performance one
> jot, so how do I get around this?

Unless the new disks are faster thean the old disk you had, RAID will not
improve your performance. What RAID does is protect you against disk
failure. That in turn requires some overhead which can decrease disk
performance. As far as I know, the only case where striping increases
performance is when you do large sequential reads or writes.

If all the disk space in the new configuration is in that one RAID array,
you have no alternatives: you will have to put the swap space on the
same disk (array) as the rest of your system. But that's not different
from your current system, so it shouldn't be a problem, should it?

Yours,
Laurenz Albe

#3 (**permalink**) 01-18-2008, 08:11 AM

Laurenz Albe writes:
> Unless the new disks are faster thean the old disk you had, RAID will not
> improve your performance. What RAID does is protect you against disk
> failure.

RAID0 provides a performance increase by striping (if the disks are on
seperate controllers). It provides no redundancy. Quite the opposite: if
either drive fails you lose all data.

> If all the disk space in the new configuration is in that one RAID array,
> you have no alternatives: you will have to put the swap space on the same
> disk (array) as the rest of your system.

He can't put his swap _partition_ on the RAID0 array without _partitioning_
it, which he does not want to do.

Install a seperate IDE disk (you obviously already have one). Put the root
and swap partitions on it. That will avoid the hassles of booting from
RAID and make recovery easier when one of your disks fails.
--
John Hasler
john@dhh.gt.org
Dancing Horse Hill
Elmwood, WI USA

#4 (**permalink**) 01-18-2008, 08:11 AM

John --

Thanks for the advice, and the clarification. Is it possible to use a
swap _file_ under Linux, and if so, what is the performance penalty,
if any?

Best regards,

Rohan Beckles
rohan.beckles@virgin.net
--
1x ASUS PC-DL Deluxe
2x Intel Xeon "Prestonia" @ 3.06GHz
1x Corsair TwinX2048-3200C2 (2x1GB)
1x Seagate Barracuda II 20GB
1x ABIT Siluro Ti4200-8x AGP 128MB DOTH OTES

#5 (**permalink**) 01-18-2008, 08:12 AM

"Rohan Beckles" <rohan.beckles@virgin.net> wrote in message
news:42f40dba$0$12882$cc9e4d1f@news.dial.pipex.com ...
> John --
>
> Thanks for the advice, and the clarification. Is it possible to use a
> swap _file_ under Linux, and if so, what is the performance penalty,
> if any?
>
> Best regards,

It's absolutely possible, and is an easy way to add or remove swap space
without having to repartition. I've seen people actually do it by preference
to avoid allocating any disk partition other than /, although I think it's a
bit excessive.

I don't know how much performance penalty there is: Since for most systems
these days, you're only using swap when you've made a mistake and are
overwhelming the system, it more acts as a buffer space to give you time and
the ability to log in and shut down the offending application without
crashing or trashing your system.

#6 (**permalink**) 01-18-2008, 08:12 AM

> Is it possible to use a swap _file_ under Linux, and if so, what is the
> performance penalty, if any?

It is possible to use a swap file. There is reportedly a performance
penalty, but I don't know how large it is. If you have enough RAM the
penalty won't matter, though.
--
John Hasler
john@dhh.gt.org
Elmwood, WI USA

#7 (**permalink**) 01-18-2008, 08:13 AM

Rohan Beckles wrote:
> Hello --
>
> As part of a sweeping system performance upgrade, I plan on migrating
> the contents of my single system disk onto two 740GD Raptors, slaved
> together as RAID0. Question: where do I put the swap partition?
> Obviously, partitioning a RAID array doesn't help performance one
> jot, so how do I get around this?

Hardware or software RAID? If software, define two swap partitions, one
per drive, and put them at the end of the available space, since
transfer rate is higher there. The O/S will use both.

If you have just a big pseudo drive, the same process applies, put the
swap partition at the outer rim (high sector numbers) for best transfer
rate.

As an example, a 50MB transfer on a fairly slow drive takes 4.605 sec on
the inner tracks, and 3.521 on the outer. That will make your system
feel more responsive (slightly) if you have low memory.

--
bill davidsen
SBC/Prodigy Yorktown Heights NY data center
http://newsgroups.news.prodigy.com

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