[Gllug] Production system - Linux 2.4.24, LVM and cciss

[Ian Northeast]

Dale Gallagher wrote:
> Hi
> 
> Ok, based on my previous post re: running 2.6 on a production system,
> and some (brief) research since then, I came to the following temporary
> conclusion, with comments.  I'd greatly appreciate feedback on this.  I
> know this post covers many topics, so I'll try to split it later,
> depending on the nature of the responses.
> 
> System:
> 
> HP Proliant DL380 Pentium Xeon 3.06GHz/533MHz/1M
> 1GB Memory (will add as necessary)
> SmartArray 6402/128MB
> 4x 72GB SCSI disks in RAID 1+0
> 2x 146GB SCSI disks for rotating backups
> 
> Software:
> 
> Slackware 9.1, Linux 2.4.x, qmail, PostgreSQL, Apache
> 
> Major considerations are:
> 
> 1.  Multifunction system requiring max performance
> 
> As everything will run (for now) on a single system, require max
> possible IO, reliability, performance, yada-yada... particularly since
> using qmail with Maildirs. So, using RAID 1+0 and possibly LVM?

Assuming you're not tight on disk space, RAID 1 will give better 
performance than RAID5 but RAID 5 will give you 50% more space as you 
have 4 disks.


> 3. LVM
> 
> Never used it, but know what a headache partition moving, symlinking etc
> can cause, so need sound advice on LVM. This system will expand to using
> external array storage at a later stage, amongst other things. I used
> Compaq Proliant boxes a few years ago and remember them requiring a
> special partition for Compaq's system utils etc - is this still the
> case?  How would I deal with this in LVM? Similarly, this consideration
> would also apply to my Dell laptop, which requires a partition for
> suspend functionality.

The IBM servers I use also have a small partition of their own, created 
by their RAID configuration software. It isn't a problem, it just exists 
on the first RAID array outside of the LVM.

As you're using Slackware I assume that the installer doesn't support 
LVM and you will have to implement it after installation. I havn't done 
this with Slackware but I have with Debian and I doubt it makes any 
difference. My servers at work use SuSE which does have LVM support in 
the installer which makes it easier, but it's not been difficult on the 
Debian machines at home.

My preference in such a case is to leave root in a partition. This saves 
having to bother with an initrd to get the LVM started up before root is 
mounted. As long as all the usual filesystems like /usr, /var, /tmp if 
it is not a symlink to /var/tmp, /opt, /home are separately mounted root 
doesn't need to change in size a lot. If you allocate 200MB to it it 
will be comfortable. If you do decide to put root in an LV, you should 
still leave /boot in a partition. You don't want the LVM moving the 
kernel around on the disk.

You have plenty of disks. So I recommend installing with just root (and 
the Compaq partition if you need it) on the disk you intend the system 
to end up on and everything else on another. Then you can create a PV in 
the remaining space on the system disk, create a VG containing it, 
create LVs for all your filesystems and swap space, boot into single 
user and move them all over.

Make sure that there is an initialisation script in place to start up
then LVM before booting back into multi user. Debian does this when 
installing the LVM software, I don't know about Slackware.

Use a filesystem type which can be enlarged such as reiserfs or you lose 
a lot of the benefits of LVM.

> Is is really viable to use LVM and a single underlying partition on the
> disk array in terms of reliability/performance etc?

It's never been a problem on my servers. And I don't think it would be 
viable to run them without LVM, people would not put up with the outages 
needed for filesystem maintenance.

Regards, Ian



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