[Gluster-users] Gluster on a Xen cloud - Questions

[Paul Hieromnimon]

Thanks for your response, Nathan.

 3. Use Gluster for redundancy instead of RAID.  It would be nice if I can
>> lose any single hard drive and/or entire server and still have access to
>> 100% of all the data in the pool.  In this sort of setup, is it possible
>> to
>> limit the number of copies of data to 2 or 3, or if I have 10 machines,
>> will
>> I be forced to have 10 copies of the data?
>>
>
> Sure, you can do almost anything you want, today there is not RAID like
> functionality, but that is on the roadmap. We use "replicate" on pairs of
> servers and then unify them together with "distribute".
>
> An example of our 4 node test cluster is:
>
> http://share.robotics.net/glusterfs.vol
> http://share.robotics.net/glusterfsd.vol
>

If you replicate pairs of servers, how come you're still using RAID 6?

>
>
>  4. Get good performance.  Will i get acceptable performance through
>> gigabit
>> ethernet, or do I need 10 gigabit ethernet or infiniband to have something
>> decent?  Because I want a configuration where each machine is both a
>> client
>> and a server, will performance degrade as I add more machine such that the
>> network needs to handle n^2 connections, where n is the number of servers?
>> Or will performance improve because data will be striped across a lot of
>> machines?
>>
>
> Infiniband is totally worth it, stuff is low cost (even can pick it up on
> ebay like we did) and has much lower latency then ethernet.
>
> Now as far as "good performance" this is where I am having the most issues
> with Gluster. To make it work with xen you need --disable-direct-io-mode
> when you start up glusterfs. I am not saying this is the best way to test,
> but if you "dd if=/dev/zero of=test bs=1G count=8" we get:
>
> XFS partition on 3ware          378 MB/s Not bad for writes!
> Gluster default                 110 MB/s Expected more...
> Gluster disable-direct-io-mode   22 MB/s OUCH!!!
>
> The other issue we have is that we have so far only been able to use zen
> with file and not tap:aio (it stars, but never finishes domu boot).
>

I saw the note in the technical faq about --disable-direct-io-mode.  What
does this do, and why is it needed to perform Xen migration?
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