Re: [Xen-users] Linux software RAID1 (Dom0 or domU)?

[Matthew Wild <M.Wild@xxxxxxxx>]

On Friday 02 February 2007 00:48, Javier Guerra wrote:
> On Thursday 01 February 2007, Jensen Nathan A Capt USAFA/DFCS wrote:
> > My fear is:
> >
> > 1.  I am totally hosed if my RAID server tanks
>
> the 'standard' answer would be: "do a mirror (RAID 1) of your RAID boxes";
> but i think this could be interpreted at least two ways:
>
> A)
> - set your RAID servers in pairs
> - use md to do RAID1 of each pair
> - each RAID1 (of two RAID servers) is one PV in your big VG
>
> .... but it's not clear 'who' does that RAID1
>
> B)
> - each RAID server is one PV in your big VG
> - create two LVs for each volume you want, make sure they're on different
> PVs - do a RAID1 of those two LVs
> - feed that RAID1 device to Xen
>
> since each volume is used only by one DomU at a time, it's clear that each
> RAID1 is responsibility of only one Dom0
>
> .... but i don't think md can take a pair of LVs to create a RAID1
>
> so i wonder, can EVMS do it? i guess it can do something like (B), but
> don't know it by heart

or 

C)
 - build pairs of RAID servers
 - replicate storage with drbd
 - create LVs on the storage and
 - export to dom0's using iSCSI or AoE...

This gives you redundancy of storage, though you'll still need some form of 
backup to deal with any potential filesystem corruption, as drbd replicates 
everything. Live migration works well as all the xen servers connect to the 
iSCSI/AoE devices permanently and you've got a consistent device naming 
scheme for the vdb's in the vm configs.

Our setup is two 16-disk RAID storage boxes running drbd and iscsitarget and 
multiple xen boxes running open-iscsi in dom0. Eventually, the storage boxes 
will end up in different buildings to allow for low level power outages and 
problems with the laboratory infrastructure. The Xen boxes could be anywhere 
on site.

Matthew
-- 
Matthew Wild                       Tel.: +44 (0)1235 445173
M.Wild@xxxxxxxx                    URL http://www.ukssdc.ac.uk/
UK Solar System Data Centre and
World Data Centre - Solar-Terrestrial Physics, Chilton
Rutherford Appleton Laboratory, Chilton, Didcot, Oxon, OX11 0QX

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