RE: [Xen-API] cross-pool migrate, with any kind of storage (shared or local)

[George Shuklin <george.shuklin@xxxxxxxxx>]

Well... 

Some about contras.

> Con: we do need to write something to manage a drbd instance, which
may be on a shared host (eg vanilla Debian dom0)

I think we can create some pre-reserved area like we do for management
(MGT LVM). It not really large space (in sectors):

Ms = [ C/262144 ] x 8 + 72

So if we limit VDI to 2TiB size it will be about 64Gb. Not very small,
but not really big. 

Or we can request to supply VDI for cross-domain migration manually (if
we could not create it automatically). For example, if we do cross-pool
migration from shared storage to shared storage we can use local drives
for drbd metadata.

DRBD manual points exact formula for size, so we can ask user for well
known size of temporary vdi.

Selection of network, I think, again, is question for user: we can not
predict where load is less critical. By default management network
(where memory is copied during migration) is reasonable default.

(And note: we can allow user to supply as a speed of replication! - it
can be changed online during replication process).


...

I'd like to note one more important question. 

When we talk about 'pool' - we assume same site with fine networking,
dedicated network to storage and so on.

But cross-pool migration is differ. It even can happen between different
sites (f.e. from NY to Paris datacenter) via unprotected networks.

Yes, we can say 'protect network by some network-level security
mechanism', but it will be very hard for some people to do.

For example: migration from one datacenter to other from dedicated
server (local storage). In this case establishing a secure connection
will be really hard - and optional security (for example via stunnel)
will be very attractive feature (not just cross-pool migration, but
'secure cross-pool migration via unprotected WAN'). It not needed to be
enabled by default (due high CPU load) but can be really useful for some
users (and as far as I know is not really require especial efforts: XCP
has used stunnel for internal purposes already). 


Ð ÐÐÐ, 18/07/2011 Ð 16:25 +0100, Dave Scott ÐÐÑÐÑ:
> There are now 2 pages on the xen wiki:
> 
> http://wiki.xensource.com/xenwiki/CrossPoolMigration
> 
> and
> 
> http://wiki.xensource.com/xenwiki/CrossPoolMigrationV2
> 
> The V2 page has a first cut at a list of pros and cons of DRBD vs 
> snapshot/copy.
> 
> Cheers,
> Dave



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