[mythtv-users] How much RAM for a 'Xen' backend-only virtual server

Gordon McLellan gordonthree at gmail.com
Mon May 5 17:11:52 UTC 2008


Yikes, 1g of ram is awful tight for a _server_ of any kind, let alone
a virtualization host!

If the xen host is "only" running the mythbackend (which also means
it's running mysql), why does it need to be virtual?   You mention
you're already running mysql for something else, why can't the myth
database be hosted on that instance too?

I'm running mythbackend as a domu on my server, and I have allocated
it 1g of ram and 2 vcpus, with Dom0 having 8g of ram and a quad core
Xeon.   Linux appears to be using most of that 1g as buffers and
cache, but that is important, since disk io on a virtual machine, and
disk io in general, is terribly slow, and a database should run from
ram if at all possible.

# free -m
             total       used       free     shared    buffers     cached
Mem:          1024        904        119          0          8        257
-/+ buffers/cache:        638        385
Swap:          509          0        509

Running top and sorting by memory usage shows httpd as the biggest hog
of ram, all ten of it's children claiming 45mb of ram each, the yum
update daemon claiming 72mb, mythbackend claiming 39mb, and mysqld
claiming 41mb.  I forget how to tell how much of the db mysql has
cached in memory, so I'll have to report back on that.  In summary, I
think my allocation of 1gb is excessive, but I've got the memory to
waste on it, so what the hay.

My setup worked perfectly for months and months with .20-1 (i think),
but since upgrading to 20-2 and now 21, my uptime has been slashed to
days at best.   I don't know if there's more network IO occuring or
what, but between the front and backends, I'm dealing with a lot of
crashes related to networked file systems.  I'm beginning to
reconsider my use of virtualization at all, since I'm still having
stability issues related to network storage problems.   My myth
network used to use NFS, and that would regularly crash, almost daily.
 After a few nfs crashes, it would leave the Dom0's kernel hosed and I
would have to do a hard reset on the box.   I've since switched to
CIFS and enjoyed nearly a week of uptime before CIFS left Dom0's
kernel hosed and again, another hard reset.


Hope this helps!
Gordon



On Mon, May 5, 2008 at 11:27 AM, James Buckley
<xanium4332 at googlemail.com> wrote:
> Hi all,
>
> Just wondering the minimum amount of RAM I should dedicate to a mythtv
> backend. As it's running in a Xen DomU, it'll be the only service runninng
> (Gentoo Linux).
>
> I only have 1G of RAM in the server, and it's acting as my router, mail
> server, web server, mysql + postgres + ldap database server, so RAM's
> starting to get tight.
>
> Cheers, James
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