[DRBD-user] SAN, drbd, ha, shared disks, ataoe, iscsi, gnbd

Alex linux at vfemail.net
Tue Aug 12 18:03:17 CEST 2008

Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.

> > sda and sdb are block devices imported via iscsi from computer1 and
> > computer2.
> >
> > Question: is possible to group sda and sdb using raid1 software in an
> > array (/dev/md0) and after that, on top of md0 to create a logical volume
> > and run GFS?
> >
> > AFAIK THIS DESIGN IS IMPOSSIBLE because raid software on linux is NOT
> > CLUTER-AWARE? So, just using iscsi (or gnbd) to export volX is NOT ENOUGH
> > because if i am loosing one computerX i am loosing all data on GFS!
> > Right?
> RedHat's LVM documentation appears to suggest that you can let LVM do the
> mirroring, and that LVM is cluster-aware (clvmd).

I didn't know that LVM can do mirroring...

> I've certainly used LVM in an RH-CS cluster, and it works pretty well.
> Talking that a step further, it _appears_ that you could configure a cLVM
> mirror over those two devices, then run GFS over the top, but I'd really
> want to test that before I believed it, let alone trusted it.

I'll be glad to make this tests but looking in lvm documentation, they are 
very vague about lvm2 mirroring. 

All i can find is just about striping:
pvcreate /dev/sda /dev/sdb
vgcreate vg_strip /dev/sda /dev/sdb
lvcreate -L 400M -i 2 -n lv_strip vg_strip
mkfs.gfs ...  /dev/vg_strip/lv_strip

How can i do lvm mirroring between sda and sdb? Can you give me an example?

For mirroring, they are saying that i need 3 devices (two for the mirror 
devices and  one for the disk, else, mirror will be reconstructed at each 

Because i don't know which will be the 3rd device, will be ok to use:

pvcreate /dev/sda /dev/sdb
vgcreate mirrorvg /dev/sda /dev/sdb
lvcreate -L 1G -m1 -n mirrorlv mirrorvg /dev/sda /dev/sdb

In order to create 1GB mirrored logical volume on each sda and sdb?


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