[CentOS] LVM and hotswap (USB/iSCSI) devices?
Simen Timian Thoresen
simentt at dolphinics.no
Sun Aug 31 16:28:23 UTC 2008
Simen Timian Thoresen wrote:
> nate wrote:
>> Simen Timian Thoresen wrote:
>>
>>> So - with the LV unmounted, I power my USB-device down, and then back
>>> up;
>>
>
> Hi Nate,
>
>> I believe your problem is you didn't deactivate the logical
>> volume, and export the volume group before disconnecting.
>
> Yes! Thank you - exporting and then importing again after replugging
> worked.
>
> I'll have to read up on what actually happens here .-)
>
> Still - say that the USB (or iSCSI) PV is not exported before being
> unplugged (cables tripped over, internet connection going down, etc) -
> how do I recover from an unplugged but not exported PV/VG? It seems that
> vg[im/ex]port only fiddle with the off-PV metadata. Is this correct?
>
> I think I'm looking for a force-import that allows me to bring a VG with
> associated LVs up provided that the PVs are present - affectively a
> 'assemble' ala mdadm.
Hah! I got this one on my own.
After unplugging, I removed the /etc/lvm/archive/ /etc/lvm/backup and
/dev/mapper/<device> entries, and then replugged;
[root at kasse ~]# pvscan
PV /dev/iscsi_01 VG iscsistorage lvm2 [102.79 GB / 102.59 GB free]
Total: 1 [102.79 GB] / in use: 1 [102.79 GB] / in no VG: 0 [0 ]
(this I've seen before)
Thinking that I could import the VG, I found that it's impossible to
imoport a non-exported VG;
[root at kasse ~]# vgimport -a
Volume group "iscsistorage" is not exported
...but just setting it active worked;
[root at kasse ~]# vgchange -a y iscsistorage
1 logical volume(s) in volume group "iscsistorage" now active
[root at kasse ~]# lvdisplay
/dev/mapper/iscsistorage-lv1: open failed: No such file or directory
/dev/mapper/iscsistorage-lv1: open failed: No such file or directory
--- Logical volume ---
LV Name /dev/iscsistorage/lv1
VG Name iscsistorage
LV UUID mKP1DG-Pc1q-vFzf-sR9v-RE3e-ChNV-T0dWq1
(...)
...and the LV is not mountable;
[root at kasse ~]# mount /dev/iscsistorage/lv1 /mnt/
mount: special device /dev/iscsistorage/lv1 does not exist
To remove the missing /dev/mapper entries, I exported and then
reimported the VG;
[root at kasse ~]# vgexport -a
Volume group "iscsistorage" successfully exported
[root at kasse ~]# vgimport -a
Volume group "iscsistorage" successfully imported
[root at kasse ~]# lvdisplay
--- Logical volume ---
LV Name /dev/iscsistorage/lv1
VG Name iscsistorage
LV UUID mKP1DG-Pc1q-vFzf-sR9v-RE3e-ChNV-T0dWq1
(...)
[root at kasse ~]# mount /dev/iscsistorage/lv1 /mnt/
[root at kasse ~]# ls /mnt/
lost+found
(...)
Woila!
I think I saw someone doing something to /dev/mapper/control as well to
skip the export-reimport steps.
I'll see if I can robustify this a little, but if this works, I'll be
significantly closer to my main goal.
Thank you again for your help .-)
Yours,
-S
> Thank you for pointing me in the right way ;-)
>
> -S
>
>> lvchange -a n <path to lvm>
>> vgexport -a (don't worry it will only export groups that are
>> ready to be exported)
>>
>> Now you can safely power the device down(provided the VG was
>> successfully exported, all logical volumes must be unmounted
>> and deactivated before it will succeed).
>>
>> when you power it back up run
>>
>> pvscan
>> vgimport -a
>> lvchange -a y <path to lvm>
>>
>> LVM is very useful for volumes that change device names, but you
>> must use it properly otherwise bad things will happen as you
>> saw.
>>
>> If you want to have USB mount automatically it may be better
>> to put a label on the file system, at least in Debian(don't
>> have a CentOS system with a USB disk handy here) the volume
>> is mounted as /media/<disk label> if there is a disk label.
>> You can use the e2label command to label the device. I'd
>> expect CentOS to likely behave similarly to debian in this
>> respect.
>>
>> nate
>>
>>
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>>
>
>
--
Simen Thoresen, Dolphin ICS
Systems Administration and Wulfkit Support
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