Software RAID5 and LVM(EVMS)

JeffBlair · Posted: Wed Jul 13, 2005 3:56 pm Post subject: Software RAID5 and LVM(EVMS)

Ok, here is the deal. I have tried to look for an answer, but I didn't see one out there. I just got a new server, HP LC2000, and I have 4 9.1 drives in it now. I am getting 6 18 gig drives in the next few weeks. My question is this. I want to be able to have a RAID-5 and either LVM or EVMS setup. I like LVM because I can increase my storage if I need to. And, I like RAID 5 for the backup. Can I have both on the same system? i.e. If a hard drive fails can I replace it without losing any data? I know if I have just a regular RAID 5 system, then I can. If it is LVM only then no. What are y'alls thoughts?

HackingM2 · Posted: Fri Jul 29, 2005 1:26 am Post subject:

I currently have a very similar setup. I use four SATA drives with differing RAID levels with LVM on top of RAID5.

You can follow this how-to, just make a RAID5 array for your main partition instead of whatever they use... I also used RAID5 for my root partition but went with RAID10 for my swap space.

http://gentoo-wiki.com/HOWTO_Gentoo_Install_on_Software_RAID_mirror_and_LVM2_on_top_of_RAID

NOTE: You will have to use RAID1 for the boot partition. Until the kernal is loaded there is no RAID driver present so RAID1 is the only thing which will work. By the time you can write to the boot partition the kernel is loaded and mirroring will work fine. During the grub/lilo and kernel-loading phase of the boot process only one device is used. Some motherboards can be set to boot from each HDD sequentially and grub can be set to try the next device as a fallback so boot redundancy is possible.

Just don't try to put too much on the LVM part. Things like etc and some others must be on the non-LVM root partition or you will need to use initrd or initramfs.

If you want an even more flexible setup I believe it can be done the other way around, RAID on LVM, which has the advantage that you can create LVM partitions using differing RAID levels, rather than deciding on one at the start. I've never tried this but I believe there are some issues with the ordering of driver initialisation.