Re: [linux-lvm] lvm2 *TEMPORARY* PV failure - what happens?

[Ming Zhang <mingz@ele.uri.edu>]

my 2c. fix me if i am wrong

either activate the VG partially, and then all LVs on other PVs are
still accessible. I remember these LVs will only have RO access. Though
I have no idea why.

use dm-zero to generate a fake PVs and add to VG, then allow VG to
activate and access those LV. But i do not know if you access a LV that
is partially or fully on this PV, what will happen.

Ming


On Tue, 2006-04-25 at 13:08 -0600, Ty! Boyack wrote:
> I've been intrigued by the discussion of what happens when a PV fails, 
> and have begun to wonder what would happen in the case of a transient 
> failure of a PV.
> 
> The design I'm thinking of is a SAN environment with several 
> multi-terabyte iSCSI arrays as PVs, being grouped together into a single 
> VG, and then carving LVs out of that.  We plan on using the CLVM tools 
> to fit into a clustered environment. 
> 
> The arrays themselves are robust (RAID 5/6, redundant power supplies, 
> etc.) and I grant that if we lose the actual array (for example, if 
> multiple disks fail), then we are in the situation of a true and 
> possibly total failure of the PV and loss of it's data blocks.
> 
> But there is always the possiblity that we could lose the CPU, memory, 
> bus, etc. in the iSCSI controller portion of the array, which will cause 
> downtime, but no true loss of data.  Or someone may hit the wrong power 
> switch and just reboot the thing, taking it offline for a short time.  
> Yes, that someone would probably be me.  Shame on me.
> 
> The key point is that the iSCSI disk will come back in a few 
> minutes/hours/days depending on the failure type, and all blocks will be 
> intact when it comes back up.  I suppose the analagous situation would 
> be using LVM on a group of hot swap drives and pulling one of the disks, 
> waiting a while, and then re-inserting it.
> 
> Can someone please walk me through the resulting steps that would happen 
> within LVM2 (or a GFS filesystem on top of that LV) in this situation?
> 
> Thanks,
> 
> -Ty!
>