Re: [Xen-devel] databases and xen?

[Kip Macy <kmacy@xxxxxxxxxxx>]

On Tue, 18 Jan 2005, Nicholas Lee wrote:

> On Tue, Jan 18, 2005 at 04:02:01AM +0200, Moshe Bar wrote:
> > I have run Mysql and Oracle 9i without any problems on 2.0.0 and 2.0.1
> > , but I didn't have LVM (don't think that would create problems)
>
> I would have thought that using loopback/file or NFS VBD would have
> caused performance issue and lost of database guarantees.

It definitely causes performance degradation, but that is certainly not
the only way to set a domain up, merely the cheapest. The I/O syncer is
all going to be managed from DOM0, so if the guest crashes
transactional integrity is maintained. If the HW crashes you have the
same issues as with ext2. If you want integrity guarantees and high
performance you'll likely want a fibre channel device exported to the
guest.


> Or does a fsync on a File VBD get pushed though to the host (dom0)?
There is no fsync on a block device. An I/O should only be acknowledged
when the device commits it. Nonetheless, on Linux I would wager that it
stays in the buffer cache until the syncer gets around to flushing it.



                                -Kip



>
> Nicholas
>
>
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