[CentOS] Questions about software RAID, LVM.

Robert Heller
Mon, 04 Feb 2013 23:40:56 -0000

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:

Disk /dev/sda: 160.0 GB, 160041885696 bytes
255 heads, 63 sectors/track, 19457 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *           1         125     1004031   fd  Linux raid autodetect
/dev/sda2             126       19457   155284290   fd  Linux raid autodetect

Disk /dev/sdb: 160.0 GB, 160041885696 bytes
255 heads, 63 sectors/track, 19457 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

   Device Boot      Start         End      Blocks   Id  System
/dev/sdb1   *           1         125     1004031   fd  Linux raid autodetect
/dev/sdb2             126       19457   155284290   fd  Linux raid autodetect

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

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 at deepsoft.com
Deepwoods Software        -- http://www.deepsoft.com/
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