[Xen-users] Re: iSCSI and LVM

[Ferenc Wagner <wferi@xxxxxxx>]

"Jonathan Tripathy" <jonnyt@xxxxxxxxxxx> writes:

>> You can use live migration in such setup, even safely if you back it
>> by clvm.  You can even live without clvm if you deactivate your VG on
>> all but a single dom0 before changing the LVM metadata in any way.  A
>> non-clustered VG being active on multiple dom0s isn't a problem in
>> itself and makes live migration possible, but you'd better understand
>> what you're doing.
>>
>>> Can you please explain to me how my plan is ambitious? Can someone
>>> please suggest where I should cut down/ scale up?
>>
>> Even 100 domUs on a single dom0 is quite a lot.  100 Mbit/s upstream
>> bandwidth isn't much.  You'll have to tune your iSCSI carefully to
>> achieve reasonable I/O speeds, which is limited by your total storage
>> speed.  Even if your domUs don't do much I/O, 128 MB of memory is
>> pretty much a minimum for each, 128 of those require 16 GB of dom0
>> memory (this is probably the easiest requirement to accomodate).
>  
> Can you please explain the steps I would need to take in order to
> connect multipl clients to a single iSCSI target?

No steps necessary, this is the usual mode of operation.

> I was thinking of using LVM on the storage server to split my RAID
> array in 2 big LVs, and then export one LV to a node. Then the xen
> node would use LVM within this exported LV. to split it up into small
> LVs for the DomUs. Is this a good or bad idea?

You can do this if you aren't interested in live migration.  Otherwise,
I find it pointless.

> The 100 Mbit/s upstream is for the internet connection. The bandwidth
> to the iSCSI server is dual bonded gigabit ethernet. What tuning could
> i do to the iSCSI setup?

MTU, number of outstanding requests, just to name a few.  Google for it.
And for all the rest as well.  I think you aren't well prepared for this
task yet, be very careful.
-- 
Regards,
Feri.

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