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RedHat Linux boot from SAN - separate boot/root devices?

 
Simon Hargrave
Honored Contributor

RedHat Linux boot from SAN - separate boot/root devices?

I'm in to process of migrating a load of RedHat servers to boot from SAN. I'd like to publish a 50Gb LUN to each host for the operating system.

Looking at some boot from SAN documentation, such as the one below, it suggests: -

"It is recommend to have separate devices for the /boot and root (/) partitions."

Why is that? Does anyone actually do that? It seems silly to me to publish a separate device for /boot, especially on EVA where the minimum LUN size is 1Gb!

Is this just an old hangup from the days of pre-LBA and 1024 cylinders?

http://www.google.co.uk/url?sa=t&source=web&ct=res&cd=6&url=http%3A%2F%2Fbizsupport2.austin.hp.com%2Fbc%2Fdocs%2Fsupport%2FSupportManual%2Fc01513866%2Fc01513866.pdf&ei=t-LuSfHjHOXPjAeSmbEO&usg=AFQjCNGbn2H5cWEpygjE0z9Ix5acbLYCoQ&sig2=Sv7lRZV9an9JjDvevsJ4ZQ
4 REPLIES
Steven E. Protter
Exalted Contributor

Re: RedHat Linux boot from SAN - separate boot/root devices?

Shalom,

For flexibility I recommend that most of the RHEL boot be LVM. RHEL can not boot from an LVM partition.

You should partition and present two LUNS to each system. First LUN should be the boot LUN.

I've never been a fan of SAN boot, due to the lack of diagnostics when there is a SAN problem.

SEP
Steven E Protter
Owner of ISN Corporation
http://isnamerica.com
http://hpuxconsulting.com
Sponsor: http://hpux.ws
Twitter: http://twitter.com/hpuxlinux
Founder http://newdatacloud.com
Simon Hargrave
Honored Contributor

Re: RedHat Linux boot from SAN - separate boot/root devices?

Our normal build (for internal drives) is that the disk is partitioned 100Mb for /boot and the rest of the disk partitioned and used by LVM.

I'm struggling to understand a real reason to publish an additional 1Gb LUN (the smallest available on an EVA8100) only to waste 900Mb of it, when having a 100Mb partition on a sole 50Gb LUN works fine.

We have to boot from SAN as we are moving them to a BladeSystem and Virtual Connect.
Tony Cicone
Honored Contributor

Re: RedHat Linux boot from SAN - separate boot/root devices?

We have great success with boot from SAN, using Redhat's multipathing or EMC's Powerpath. We do not assign a separate drive for /boot, we just carve up the boot root drive in 3 partions.

# fdisk -l /dev/sda

Disk /dev/sda: 36.2 GB, 36203397120 bytes
255 heads, 63 sectors/track, 4401 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

Device Boot Start End Blocks Id System
/dev/sda1 * 128 147 160650 83 Linux
/dev/sda2 148 2497 18876375 8e Linux LVM
/dev/sda3 2498 3541 8385930 82 Linux swap / Solaris

Then we use LVM ontop of the mulitpath or powerpath devices. We do not put swap under LVM control.

This works great for us.

Steven E. Protter
Exalted Contributor

Re: RedHat Linux boot from SAN - separate boot/root devices?

Shalom,

Make /boot 1 GB. You can use the 900 MB of space for other files.

Or drop LVM and go with a 50 GB system that can not easily be re-sized.

SEP
Steven E Protter
Owner of ISN Corporation
http://isnamerica.com
http://hpuxconsulting.com
Sponsor: http://hpux.ws
Twitter: http://twitter.com/hpuxlinux
Founder http://newdatacloud.com