Rants and Revelations

I needed to re-arrange some disk space. I explained the situation in Rants and Revelations » Why didn’t I use LVM on everything? with a table showing the current layout and everything. At the time, my plan was:

1. Migrate the content of /dev/hdc3 off using “pvmove” and “vgreduce”.
2. Delete all three partitions on /dev/hdc3 and add it back to the vg using “pvcreate /dev/hdc; vgextend xen-space /dev/hdc”.
3. Migrate the content of /dev/hde2 off using “pvmove” and “vgreduce”.
4. Delete the /dev/hde2 partition and increase the disk of /dev/hde1 to fill up the drive, and use resize2fs to make /dev/hde1 use the whole partition.

I did steps 1-3, and it all worked perfectly. I didn’t have to shut down anything, and it didn’t interrupt the normal operation of either the dom0 or the domUs. But when I’d done that, I realized I actually had enough free space on the lv that I could do an even better plan:

1. Set up a 250Gb lv.
2. Use rsync to copy everything from /dev/hde1 to the lv.
3. Once that was done, shut down domU 1.
4. Make /dev/hde1 part of the lv.
5. Make the 250Gb lv bigger using lvextend– I chose to add 100Gb to it, and I have space to add more if I need it.
6. “e2fsck -f” and “resize2fs” the lv.
7. Restart the domU 1, using the lv instead of /dev/hde1.

This worked perfectly. The domU was down about 10-15 minutes tops. /dev/hde is still partitioned into two partitions, even though both partitions are part of the same vg. But other than that, it’s exactly what I’d have done if I were setting it up from scratch now.

Due to a series of historical accidents, I have the following disk space layout:

Partition	Size	Use
Disk 1 – 250Gb
/dev/hda1	2Gb	dom0 root
/dev/hda2	2Gb	dom0 swap
/dev/hda3	Rest	part of vg “xen-space”
Disk 2 – 250Gb
/dev/hdc1	2Gb	formerly dom0 root – unused
/dev/hdc2	1Gb	formerly dom0 swap – unused
/dev/hdc3	Rest	part of vg “xen-space”
Disk 3 – 400Gb
/dev/hde1	300Gb	mounted as /dev/hdb on a domU
/dev/hde2	Rest	part of vg “xen-space”

The root partitions of the three domUs are all lvs on vg “xen-space”. There is over 250Gb free on the vg.

What I would like to do is clean up the second drive to get rid of the extraneous partitions, and to grow the partition on /dev/hde1 to the full disk. So what I’m thinking of doing is the following:

1. Migrate the content of /dev/hdc3 off using “pvmove” and “vgreduce”.
2. Delete all three partitions on /dev/hdc3 and add it back to the vg using “pvcreate /dev/hdc; vgextend xen-space /dev/hdc”.
3. Migrate the content of /dev/hde2 off using “pvmove” and “vgreduce”.
4. Delete the /dev/hde2 partition and increase the disk of /dev/hde1 to fill up the drive, and use resize2fs to make /dev/hde1 use the whole partition.

The problem is that I don’t know if I can do this stuff without shutting down the domUs. And for the physical partition /dev/hde1, which is mapped to the /dev/hdb on one of my domUs, I don’t know if I have to shut down the domU or just umount it within the domU and remount it afterwards.

The box is up. It was only offline for about 20 minutes, tops. Everything seems to be working. Fingers crossed.

I officially love LVM. And I wish my big binary file archive was on LVM, because it’s getting nearly full and I want to expand it. Of course, any changes in it will probably require shutting down because of the way the file system is mounted through Xen.

Tomorrow morning, I go out to the colo box and replace the existing one with my spiffy “new” Yellow Menace. I’ve tested the hell out of this one and it can handle all three domUs and the dom0 all doing dd’s from /dev/zero to the hard disk over and over again, which will be a nice change from the existing one freezing up throwing ext3 errors whenever I’m doing something disk intensive.

My plan is to pull out the old one, move the disks to the new one, boot it up, make sure I can log into the dom0 from home, and then go home to tinker with it. If things go as I expect, the services that live on here, like this blog, my mailing lists, my photo gallery, the Rochester Flying Club web site and others should only be off the air for an hour or so.

Then I’ll test the hell out of the old box when I get it home to see if I can reproduce the problem, and then see if I can fix the problem somehow, maybe with a new IDE cable. Then I’ll know how to advertise it on eBay – either as a working box, or a box with a suspect IDE controller but a probably fine SCSI controller.