CentOS - Feb 2008 - Install on two discs with Software Raid and LVM

I am mirroring two drives during install, what's the best practice here for
the swap partition? Maybe two separate lv's from independent vg's *not*
mirrored for swap and the let the OS manage it? Boot and the / vg will be
mirrored.

Thanks!
jlc

Create a swap lv in the vg you created out of /dev/md1, assuming /dev/md0 is
/boot.

-Ross


----- Original Message -----
From: centos-bounces at centos.org <centos-bounces at centos.org>
To: 'centos at centos.org' <centos at centos.org>
Sent: Mon Feb 04 17:29:45 2008
Subject: [CentOS] Install on two discs with Software Raid and LVM

I am mirroring two drives during install, what's the best practice here for
the swap partition? Maybe two separate lv's from independent vg's *not*
mirrored for swap and the let the OS manage it? Boot and the / vg will be
mirrored.

Thanks!
jlc

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>Create a swap lv in the vg you created out of /dev/md1, assuming /dev/md0 is
/boot.
>
>-Ross
Oh, I thought it wasn?t good to run swap inside software raid? If I was wrong, I
assume this is beneficial since if one of the HD?s tanks while its running, it
will survive the failure and not need to reboot?

Thanks!
jlc

Joseph L. Casale wrote:
> I am mirroring two drives during install, what's the best practice here
for the swap partition? Maybe two separate lv's from independent vg's
*not* mirrored for swap and the let the OS manage it? Boot and the / vg will be
mirrored.
> 
If you would like to keep running though a disk failure you need to 
mirror swap.

-- 
   Les Mikesell
    lesmikesell at gmail.com

That's old information, kernel swapper can handle all types of dev mapper
setups these days (well all types on fixed media).

-Ross


----- Original Message -----
From: centos-bounces at centos.org <centos-bounces at centos.org>
To: 'CentOS mailing list' <centos at centos.org>
Sent: Mon Feb 04 17:43:50 2008
Subject: RE: [CentOS] Install on two discs with Software Raid and LVM
>Create a swap lv in the vg you created out of /dev/md1, assuming /dev/md0 is
/boot.
>
>-Ross
Oh, I thought it wasn?t good to run swap inside software raid? If I was wrong, I
assume this is beneficial since if one of the HD?s tanks while its running, it
will survive the failure and not need to reboot?

Thanks!
jlc

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the addressee(s) named herein and may contain legally privileged
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>That's old information, kernel swapper can handle all types of dev
mapper setups these days (well all types on fixed media).
Ross and Les,
Thank you!
jlc

Joseph L. Casale wrote:
> I am mirroring two drives during install, what's the best practice here
for
> the swap partition? Maybe two separate lv's from independent vg's
*not*
> mirrored for swap and the let the OS manage it? Boot and the / vg will be
> mirrored.
More of a comment than a answer but I don't use LVM for the internal
disks on my systems, only for external disks(SAN, etc). I've found that
at least for me LVM is very problematic when used in kickstart, I get
frequent failures(python errors). So I just go with normal partitions
internally.

My software raid setup for systems that use it, is 100MB
/boot partition, a 4G swap partition and the rest of the
drive is one big root partition. All of them in software
RAID 1.

#Partition clearing information
clearpart --all
#Partition the Drives
part raid.01  --size=100 --ondisk=sda
part raid.02  --size=100 --ondisk=sdb
raid /boot --level 1 --device=md0 raid.01 raid.02

part raid.03  --size=4096 --ondisk=sda
part raid.04  --size=4096 --ondisk=sdb
raid swap --level 1 --device=md1 raid.03 raid.04

part raid.05  --size=100 --ondisk=sda --grow
part raid.06  --size=100 --ondisk=sdb --grow
raid / --level 1 --device=md2 raid.05 raid.06

Then to work around a software raid bug in anaconda in
CentOS/RHEL 4(not sure about 5, but I still do it anyways),
in my %post I do:
cat >/tmp/grub.txt <<EOF
root (hd0,0)
geometry (hd0)
setup (hd0)
geometry (hd1)
setup (hd1)
quit
EOF

grub --batch </tmp/grub.txt 2>&1 | tee /root/grub-install.txt

Without the workaround there's a high likely hood that the
system won't boot to the OS afterwards.

If you foresee frequent changes on your OS disks then LVM
is probably a good choice, I just got sick of the kickstart
failures with it.

nate

Scott Silva <ssilva at sgvwater.com> wrote:
> on 2/4/2008 2:43 PM Joseph L. Casale spake the following:
>   
>>> >> Create a swap lv in the vg you created out of /dev/md1,
assuming /dev/md0 is /boot.
>>> >>
>>> >> -Ross
>>>       
>> > 
>> > Oh, I thought it wasn???t good to run swap inside software raid?
If I was wrong,
>>     
> I assume this is beneficial since if one of the HD???s tanks while its
running,
> it will survive the failure and not need to reboot?
>   
>> > 
>> > Thanks!
>> > jlc
>>     
> That is an old assumption from the infancy of software raid, less than
optimal
>   installed ram, and slower processors. When ram was expensive, you used
more
> swap because it was cheaper. But ram is so much cheaper now that it make no
> sense to run a machine that needs to touch swap except in an emergency.
>   
Not really a valid assumption about install enough memory and swap won't 
get used. *nixes have a design feature that swaps out programs that 
aren't used "just in case" the some other program needs the space.
Sun
workstations back in the '80s and '90s used to be the worst at this. It 
was faster to shutdown at night and restart in the morning since leaving 
the system up all night would result in most everything getting swapped 
out to disk "just in case" the space would be needed. Try to use the 
system in the morning and it would be busy swapping everything back into 
RAM for quite a while.

So with 2GB of RAM on my desktop, I still see 144K of swap getting used 
with me generating very little activity as I read my e-mail. If my swap 
"went away", I would have a problem if Linux tried to swap back in 
whatever that 144k of program is. Better to have swap on a RAID volume.

Cheers,
Dave

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