evms lvm raid

carpman · Posted: Sun Jan 26, 2003 11:41 pm Post subject: evms lvm raid

Hello, i am planning to set up a nice little dual 500 box as a gentoo server, the server has 4 9gig scsi drive but no hardware raid controller.

I really want to have it setup as a raid 5, but with the drives only being small i would like to be able to expand available storage easily. I have read that LVM is good for dynamically expanding storage space but i am not sure how this fits into a raid 5 system.

Enter evms, from what i have read this should enable me to set my 4 drives as a LVM solution with raid 5, is this correct?

if so any guides about doing this?

many thanks

MacMasta · Posted: Mon Jan 27, 2003 9:36 pm Post subject:

EVMS can do it, and easily, at that.

Just fire up the install CD, go read the documentation (google it) and go.

~Mac~

blk_jack · Posted: Tue Jan 28, 2003 8:37 am Post subject:

I found that a lot of the documentation on RAID (the MD module) is quite sketchy at the moment. Post on mailinglists if you can't figure it out from the documentation you can find and be PATIENT. In the end it's well worth it. (I recently setup RAID1 with EVMS and I'm quite happy with it despite the lack of decent tutorials, FAQs and how-tos).

carpman · Posted: Tue Jan 28, 2003 1:23 pm Post subject:

Thanks for reply, yes i have looked for info by searching, lots of stuff on LVM lots of stuff on raid, but not a lot on EVMS and setting up an LVM Raid 5 with it.

I am going to wait for 1.4 final, but may join mailng list and see what they can come up with.

BigBrownDog · n00b Joined: 18 Feb 2003 Posts: 6

I too am looking for some more details on the MD/Raid support within EVMS - I work with AIX a lot at work and am pretty familiar with the concepts that EVMS provides, but exactly how the MD/Raid modules should work escape me at the moment.

I was able to build a RAID-5 set with mkraid and /etc/raidtab outside of EVMS and make it work fine. Then, when I fired up evmsgui, it seemed to autodetect the RAID disk (/dev/md0) and it created a device called /dev/evms/md/md0. When I looked at the running processes, there appeared to be 2 different kernel processes running related to RAID, [raid5mgr] and [evms_raid5mgr] (possibly not the exact names, I'm away from the system right now). Everything appeared to be working OK, but the documentation makes reference to NOT using both the native MD drivers and the EVMS RAID drivers simultaneously. Here are my questions -

1) Was this the correct order of operations to get it going?
2) If not, is there a way within EVMS to "create" the RAID device? If so, I can't find it.
3) Should both of the kernel processes be running?
4) Which device do I want to build my fs on? /dev/md0 or /dev/evms/md/md0?

Inquiring minds want to know -----
_________________
Thanks,

Matt Cleland

BigBrownDog · n00b Joined: 18 Feb 2003 Posts: 6

I think I figured it out last night - not obvious, but it seems to work. The key was that under EVMS, I couldn't create a RAID-5 region with just the raw, unpartitioned drives (/dev/sdb, /dev/sdc, /dev/sdd) as I could with the MD raidtools. I had to put a DOS Segment Manager on each disk and then create a single partition on each one via EVMS. Once I did that, I could go in a create a new Region using the RAID-5 plugin. So far it seems to work good, however the resync time is pretty long. It said it was going to take about 9 hours to resync a 3x18GB RAID-5 array -- that seems to be quite a long time. I noticed that it wasn't hitting the drives very hard, it seemed to be pacing itself quite a bit :-)

_________________
Thanks,

Matt Cleland