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?
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