On Mon, Feb 4, 2013 at 6:40 PM, Robert Heller heller@deepsoft.com wrote:

I am planning to increase the disk space on my desktop system. It is running CentOS 5.9 w/XEN. I have two 160Gig 2.5" laptop (2.5") SATA drives in two slots of a 4-slot hot swap bay configured like this:

I would certainly suggest testing these steps out in some form or another as a dry run. And verify your backups and/or create new ones ahead of time. :)

Create your new softraid mirror with the larger disks, add that device (we'll say md3 - since the new /boot will be md2 temporarily) to your existing LVM volume group, then pvmove the physical extents from the existing disk /dev/md1 to /dev/md3. Then verify that the extents have been moved off md1 and are on md3. Finally remove md1 from the VG with pvremove.

I don't recall if I specifically used these notes, but the process matches the one I used. [0] A few more bits of info I recognize from my readings a while back. [1] [2] [3]

I expect you could easily tweak your mdadm config and rebuild your initial ramdisk so that the next time you reboot there isn't an issue. This all depends on how much of this process you plan on doing online.

[0] http://www.rhcedan.com/2010/10/20/migrating-physical-volumes-in-a-lvm2-volum... [1] http://www.centos.org/docs/5/html/Cluster_Logical_Volume_Manager/move_new_ex... [2] http://tldp.org/HOWTO/LVM-HOWTO/removeadisk.html [3] http://www.whmcr.com/2011/06/21/moving-part-of-an-lvm-vg-from-one-pv-to-anot...

sauron.deepsoft.com% cat /proc/mdstat

Personalities : [raid1] md0 : active raid1 sdb1[1] sda1[0] 1003904 blocks [2/2] [UU]

md1 : active raid1 sdb2[1] sda2[0] 155284224 blocks [2/2] [UU]

unused devices: <none>

That is I have two RAID1 arrays: a small (1Gig) one mounted as /boot and a larger 148Gig one that is a LVM Volume Group (which contains a pile of file systems, some for DOM0 and some that are for other VMs). What I plan on doing is getting a pair of 320Gig 2.5" (laptop) SATA disks and fail over the existing disks to this new pair. I believe I can then 'grow' the second RAID array to be like ~300Gig. My question is: what happens to the LVM Volume Group? Will it grow when the RAID

In my experience the VG will grow by whatever extents the new PV has. I found it quite helpful to use loopback devices to test possible softraid and/or LVM scenarios.

array grows? Or should I leave /dev/md1 its current size and create a new RAID array and add this as a second PV and grow the Volume Group

Just add md3 to the VG and move the extents as noted above.

that way? The documentation is not clear as to what happens -- the VG is marked 'resisable'.

The biggest gotcha is with PVs. Example even though this doesn't apply: In that if you plan on enlarging a disk (ex: LVM backing for a VM that uses LVM), the PV in the VM has to be offline to resize (the OS doesn't recognize the larger disk until after a reboot, but cannot be resized since the PV is online again!). You avoid that pitfall since you will have a separate disk (md3) that can be hot added.

sauron.deepsoft.com% sudo pvdisplay --- Physical volume --- PV Name /dev/md1 VG Name sauron PV Size 148.09 GB / not usable 768.00 KB Allocatable yes PE Size (KByte) 4096 Total PE 37911 Free PE 204 Allocated PE 37707 PV UUID ttB15B-3eWx-4ioj-TUvm-lAPM-z9rD-Prumee

sauron.deepsoft.com% sudo vgdisplay --- Volume group --- VG Name sauron System ID Format lvm2 Metadata Areas 1 Metadata Sequence No 65 VG Access read/write VG Status resizable MAX LV 0 Cur LV 17 Open LV 12 Max PV 0 Cur PV 1 Act PV 1 VG Size 148.09 GB PE Size 4.00 MB Total PE 37911 Alloc PE / Size 37707 / 147.29 GB Free PE / Size 204 / 816.00 MB VG UUID qG8gCf-3vou-7dp2-Ar0B-p8jz-eXZF-3vOONr

-- Robert Heller -- 978-544-6933 / heller@deepsoft.com Deepwoods Software -- http://www.deepsoft.com/ () ascii ribbon campaign -- against html e-mail /\ www.asciiribbon.org -- against proprietary attachments

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Hope this helps.

Best Regards,