[linux-lvm] lvm2 and external enclosures

[linux-lvm] lvm2 and external enclosures

[Ron Johnson]

Hi,

(The purpose of this "exercise" is to implement a backup strategy.)

I created PVs then an LV on a pair of drives in a USB dual 
enclosure, created the FS, backed up my data, umounted the fs, and 
disconnected/powered down the enclosure.

Upon powering it back up/reconnecting it, I did vgscan, vgchange, 
mount, but got IO and "unable to read superblock" errors.

Rebooting, even with the external drives disconnected, made things 
all better (though I did have to do an lvchange -a y).

***** START ******

# vgscan
   WARNING: Ignoring duplicate config node: filter (seeking filter)
   Reading all physical volumes.  This may take a while...
   /dev/dm-1: read failed after 0 of 4096 at 2000380952576: 
Input/output error
   /dev/dm-1: read failed after 0 of 4096 at 2000381009920: 
Input/output error
   /dev/dm-1: read failed after 0 of 4096 at 0: Input/output error
   /dev/dm-1: read failed after 0 of 4096 at 4096: Input/output error
   /dev/dm-1: read failed after 0 of 4096 at 0: Input/output error
   Found volume group "backup_vg" using metadata type lvm2
   Found volume group "main_huge_vg" using metadata type lvm2


# vgchange -a y backup_vg
   WARNING: Ignoring duplicate config node: filter (seeking filter)
   /dev/dm-1: read failed after 0 of 4096 at 0: Input/output error
   1 logical volume(s) in volume group "backup_vg" now active


# mount -v /mnt/backups
mount: wrong fs type, bad option, bad superblock on 
/dev/mapper/backup_vg-backup_lv,
        missing codepage or helper program, or other error
        In some cases useful info is found in syslog - try
        dmesg | tail  or so


[28722.859373] EXT4-fs: unable to read superblock
[28722.859458] EXT3-fs: unable to read superblock

***** STOP *****

Any thoughts on getting lvm2 to play nice with dynamic devices?

Thanks

-- 
Scooty Puff, Sr
The Doom-Bringer

Re: [linux-lvm] lvm2 and external enclosures

[Stuart D. Gathman]

On Sun, 19 Jul 2009, Ron Johnson wrote:

> (The purpose of this "exercise" is to implement a backup strategy.)

...

> Any thoughts on getting lvm2 to play nice with dynamic devices?

You have to do "vgchange -an backupvgxx" before removing the 
dynamic volumes.  It is possible to deactivate the vg after
physical removal (which you must do before a vgscan will work),
but it was tricky - the details were posted here a while back.

I created the VG on the full physical device (/dev/sdx, not /dev/sdx1),
and liked the idea of dispensing with the crufty DOS boot sector,
and getting resizable "partitions".

But the whole process is a pain (the two levels of mount/umount/vgchange) 
- and after creating similar backup solutions at 7 sites, I finally decided
that a labeled (so it doesn't matter which device node the drive appears on)
filesystem on /dev/scx1 was the simplest and most reliable way to go.
I keep the filesystem mounted in readonly mode (users are always removing
tapes or usb drives when they aren't supposed to, "Didn't you see the yellow
light flashing???").  I do "mount  -o remount,rw /media/backup" before the
backup script, and "mount -o remount,ro /media/backup" afterward.  I do and
unmount and fsck every day - which ensures that the fs gets clean regularly.

Where USB and other hotswap drives shine with LVM is testing drive failure
recovery.  It is simple and safe (hardware wise) to disconnect a USB
drive to see how your LVM configuration handles the failure.

-- 
	      Stuart D. Gathman <stuart@bmsi.com>
    Business Management Systems Inc.  Phone: 703 591-0911 Fax: 703 591-6154
"Confutatis maledictis, flammis acribus addictis" - background song for
a Microsoft sponsored "Where do you want to go from here?" commercial.

Re: [linux-lvm] lvm2 and external enclosures

[Ron Johnson]

On 2009-07-19 23:30, Stuart D. Gathman wrote:
> On Sun, 19 Jul 2009, Ron Johnson wrote:
> 
>> (The purpose of this "exercise" is to implement a backup strategy.)
> 
> ...
> 
>> Any thoughts on getting lvm2 to play nice with dynamic devices?
> 
> You have to do "vgchange -an backupvgxx" before removing the 
> dynamic volumes.  It is possible to deactivate the vg after

Worked like a charm.  Thanks!

-- 
Scooty Puff, Sr
The Doom-Bringer