[Gluster-users] how well will this work

Miles Fidelman mfidelman at meetinghouse.net
Sun Dec 30 20:10:59 UTC 2012


Thanks for the details.  If I might trouble you for a few more...

Jeff Darcy wrote:
> On 12/30/12 1:33 PM, Miles Fidelman wrote:
>> What's the alternative, though?  Ok, for application files (say a word
>> processing document) that works, but what about spools, databases, and
>> such?  Seems like blocks are the common denominator.
> It's all blocks underneath; it's a matter of how you get to those blocks.  If
> you use a simulated block device which is actually a GlusterFS file, then
> you'll be going through both FUSE and the loopback driver.  That actually works
> OK for many things, but latency will be a bit high e.g. for databases.  One
> option is to use the qemu interface, which avoids both sources of overhead.  In
> fact, the overhead from virtualizing your database server is likely to be lower
> than FUSE+loopback because our esteemed kernel colleagues seem a lot more
> interested in making virtual I/O work better than in doing the same for FUSE.
> It's still a tiny hit compared to running a DB on bare metal, but the value of
> being able to survive a failure should more than outweigh that.

I'm running Xen virtualization, and I understand how all the pieces fit 
together for running paravitualized hosts over a local disk, software 
raid, LVM, and DRBD - but none of those involve qemu.  I wonder if you 
could say a little bit about how all the pieces wire together, if I 
wanted to mount a Gluster filesystem from a paravirtualized VM, through 
the qemu interface?

Thanks again,

Miles Fidelman

In theory, there is no difference between theory and practice.
In practice, there is.   .... Yogi Berra

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