Bart Schaefer wrote:
We have a large MySQL database currently running on a CentOS 3.x server with an external SCSI RAID device. This is currently an ext2 filesystem because it was migrated once previously from an even older RedHat system. We need to add storage capacity to this database and prepare for additional future growth. One of the options under consideration is to move to CentOS 5 and use LVM.
Of some concern is that we run some pretty heavy-duty queries against this database in close to real time, so we don't want the switch to scalable storage to have a significant impact on read latency.
Consequently I'm looking for sources of information on two topics:
- What kind of performance can we expect from an LVM group as compared
to mounting the RAID array directly?
OK, the answer to this question is ...
RAID and LVM can be used together, or individually.
If you have 2 or more drives that are the same in the machine, you can "Stripe" your LVM. When doing this it behaves similarly to RAID0 (striping with no CRC / Redundancy).
LVM done this way is quite fast ... but obviously you would need to provide another way to protect your data.
See this article for how to use LVM striping:
http://www.redhat.com/magazine/009jul05/features/lvm2/
http://www.tldp.org/HOWTO/html_single/LVM-HOWTO/#recipethreescsistripe
Obviously, LVM with striping is faster than a normal LVM setup.
- What's involved in migrating our filesystem from ext2 to LVM with a
minimum of downtime?