[Linux-cluster] GFS and CLVM-snapshot

[Kenji Wakamiya]

Hello,

I have some basic questions.
I'm using GFS with the following configuration.

  node1  node2  node3 (FC3)
   GFS    GFS    GFS
   LV     LV     LV   <-- CLVM
  GNBD   GNBD   GNBD  <-- gnbd_import -n
   |      |      |
   +------+------+
          |
         GNBD  <-- gnbd_serv -n / gnbd_export -c
         node0 (file server: FC3)

Only for snapshot and backup, CLVM has been introduced here.
Is a setup such as this correct?
If so (or not :), why "sometimes" the following error occor?
Don't I need freeze/unfreeze GFS manually, like XFS?

  (on any node of node1-3)
  # gfs_tool freeze /mnt/gfs
  # lvcreate -s -n lv0ss0 -L 2G /dev/vg0/lv0
    Logical volume "lv0ss0" created
  # gfs_tool unfreeze /mnt/gfs
  # mount -t gfs -o ro,lockproto=lock_nolock /dev/vg0/lv0ss0 /mnt/gfs-ss
  mount: cannot mount block device /dev/vg0/lv0ss0 read-only

But if once I did gfs_fsck, the read-only mount succeeds.
Should I always do gfs_fsck before to use a snapshot?

  # gfs_fsck /dev/vg0/lv0ss0
  Initializing fsck
  Starting pass1
  Pass1 complete
  --snip--
  Starting pass5
  Pass5 complete
  # mount -t gfs -o ro,lockproto=lock_nolock /dev/vg0/lv0ss0 /mnt/gfs-ss

But on rare occasions, gfs_fsck also cause some errors.
For example,

  # gfs_fsck /dev/vg0/lv0ss0
  Initializing fsck
  Buffer #1736310 (1 of 4) is neither GFS_METATYPE_RB nor GFS_METATYPE_RG.
  Resource group is corrupted.
  Unable to read in rgrp descriptor.
  Unable to fill in resource group information.

The origin and snapshot LVs are as follows.

  # lvdisplay
    --- Logical volume ---
    LV Name                /dev/vg0/lv0
    VG Name                vg0
    LV UUID                fVPY4J-cndk-YD5n-wU0m-QR0S-2txI-LvnnQ5
    LV Write Access        read/write
    LV snapshot status     source of
			   /dev/vg0/lv0ss0 [active]
    LV Status              available
    # open                 1
    LV Size                20.00 GB
    Current LE             10240
    Segments               1
    Allocation             inherit
    Read ahead sectors     0
    Block device           253:0

    --- Logical volume ---
    LV Name                /dev/vg0/lv0ss0
    VG Name                vg0
    LV UUID                hZea21-flge-bI5J-gcCy-pKug-0YHN-ZXR7I4
    LV Write Access        read/write
    LV snapshot status     active destination for /dev/vg0/lv0
    LV Status              available
    # open                 1
    LV Size                20.00 GB
    Current LE             10240
    COW-table size         2.00 GB
    COW-table LE           1024
    Allocated to snapshot  2.35%
    Snapshot chunk size    8.00 KB
    Segments               1
    Allocation             inherit
    Read ahead sectors     0
    Block device           253:4

[Version info]
      Linux: 2.6.11-1.14_FC3smp
GFS/Cluster: CVS head of about 08 April (with CMAN/DLM)
 Dev-Mapper: 1.01.01 / CVS head of about 03 May
       LVM2: 2.2.01.09 / 2.2.01.10
       (--disable-selinux --with-clvmd=cman --with-cluster=shared)

Thanks, and sorry for my broken English.

-- Kenji