Re: multiple swap areas and RAID 1

[Gary Dale <garydale@rogers.com>]

On 08/08/12 01:45 PM, Georgi Naplatanov wrote:
> On 08/08/2012 08:14 PM, � wrote:
> > On Wed, 08 Aug 2012 16:25:01 +0300, Georgi Naplatanov wrote:
> >
> > > I'm going to configure Debian GNU/Linux with software RAID 1 and I 
> > > think
> > > to put swap area on RAID 1 (/dev/mdX), but someone told me that if the
> > > computer have multiple swap partition (e.g. /dev/sda2, /dev/sdb2) with
> > > equal priorities, linux kernel will mirror swap area between different
> > > devices. Is that true ? I mean kernel 2.6.32 and 3.2.x.
> >
> > I guess you mean these two different approaches:
> >
> > 1. Swapping on RAID
> > https://raid.wiki.kernel.org/index.php/Why_RAID%3F#Swapping_on_RAID
> >
> > 2. More on Linux RAID: Swap On RAID?
> > http://blog.taggesell.de/index.php?/archives/53-More-on-Linux-RAID-Swap-On-RAID.html 
> >
> >
> > I'd go for the second: put swap under a raid-1 device; without going too
> > much deep into the issue, it makes more sense to me.
> >
> > Greetings,
>
> Hi Camaleón.
>
> I did so - put swap on RAID 1.
>
> I haven't found information about linux kernel possibility of 
> mirroring swap automatically so this is probably misunderstanding or 
> mistake.
>
> Best regards
> Georgi
The basic issue is that putting swap on RAID slows down the writes but 
can speed up reads. However, because of the error checking and 
correcting, it's safer. You can also use swap files instead of swap 
partitions. The speed difference isn't noticeable anymore and swap files 
are more flexible.