Re: [Xen-users] Xen and iSCSI

[Markus Hochholdinger <Markus@xxxxxxxxxxxxxxxxx>]

Hi,

Am Montag, 30. Januar 2006 03:57 schrieb Alvin Starr:
> Markus Hochholdinger wrote:
> >Am Sonntag, 29. Januar 2006 22:58 schrieb Alvin Starr:
> >>Markus Hochholdinger wrote:
> >>We are doing doing this. Well sort of.
> >>We are having the dom0 attach to the iscsi devices and then pass them up
> >>as hda/hdb. The domU's deal with the raiding of the devices.
> >And the domU makes the raid1?
> Yes.

so i will not be the only one who will do the raid1 in domU.


[..]
> >But you have to take care that no two dom0s write to the same iscsi
> > target!
> I have burned myself there more than a few times.

Sounds very bad.


> Currently I use the vmid as a unique handle. I have a simple mapping
> between vmid and iscsi device and I use the vmid to create the MAC
> address of the domU.
> My quick hack idea is to ping and see if a domU has taken the MAC
> address and if so then  I will not start the new domain.
> It would be really nice if Xen had some global idea of what domains are
> running that would make most of these problems go away.

Yes! Thats a big point. Perhaps someone would try to make a automatic fail 
over if one Xen host dies and starts a domU on another Xen host. But if domU, 
at what reason ever, is not dead you mess up your fs! And on a production 
system this will really be bad!


> >>I have done the resync thing to upgrade the storage server software. It
> >>is a pain but it is do-able.
> >Sounds not that good i hoped.
> The process is workable and I was able to keep 8 domains running on 3
> systems for my switch over and back.

A little raw calculation:
 - 1 TByte (1000 GByte) disk space on each storage server
 - 1 GBit/s LAN (~ 100 MByte/s)
 => complete resync will last about 3 hours

So i saw hardware raid controllers takeing longer for much lesser disk space!

[..]

-- 
greetings

eMHa

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