[mythtv-users] WAY OT: Storage designs

Greg Oliver oliver.greg at gmail.com
Mon Aug 30 00:24:40 UTC 2010


On Sun, Aug 29, 2010 at 7:08 PM, Tyler T <tylernt at gmail.com> wrote:
> I wanted to do iSCSI for my remote FE. At the time, the version of the
> iSCSI initiator that shipped with my distro of choice was broken so I
> reluctantly used NFS. However, now that I've been forced to used NFS
> against my will, I think I've been converted to it: it's really
> convenient to hop on my BE and be able to alter files at will on the
> FE's filesystem. I realize you can mount an iSCSI image on loopback to
> do this too, but not while the FE is booted (unless using an exotic
> fs). Also, if you have multiple FEs, you can softlink all the files in
> the rootfs over to another directory and then unlink just a few config
> and log files that are unique to each FE. This saves quite a lot of
> disk space (and gives a performance increase -- if one FE accesses a
> file, it gets put into the read cache, so other clients requesting the
> same data enjoy less latency).

Yes, this is what I am currently doing, and while it works well, I am
just looking for what is fastest..  I have not been impressed with
either CIFS or NFS speeds compared to iSCSI at work..  That may be
entirely different with NFS4 like I said - we do not have that rolled
out on our clusters in the lab to try it - so I'll do it at home..  :)

> The other nice thing about NFS is installing your OS. If your distro's
> installer doesn't ship with an iSCSI initiator, getting a fs installed
> onto iSCSI can be a bit of a hassle (i.e., installing to something
> like a USB thumb drive, then 'dd'ing over to the iSCSI target). NFS,
> on the other hand, is well-supported by my distro's installer so
> installation was exactly one mount command more complicated than
> installing to a local HD.

I build all of my netboot images in a chroot on the server, so just
serving it up after I compress it..  Never have to go to a frontend..

> Swap is one sticky point with NFS though. I ran my 0.21 FE with 256MB
> RAM and no swap for over a year without issue, though. My current 0.23
> FE has 384MB RAM and no swap; still no problems as of yet. (Obviously,
> this won't work well if you're going to do other things with your FE
> besides watch recordings and rips, like web browsing.) In this case
> perhaps an iSCSI swapfile can supplement the NFS rootfs.

Yeah - I use no swap either.  I'll never use it for more than a FE either..

> Don't get me wrong, I still like the idea of using iSCSI rootfs for
> FEs, for performance and for "aesthetic" reasons. I just find myself
> an unexpected NFS fan.

I'll use whatever yields the best performance (more for my backups
than the FEs)..  The FEs run just fine over NFS, but doing rsyncs can
be painful - especially if I have created more virtual machines for
work, and need to transfer 100+GB over the network...

There's also no reason I could not run them both simultaneously and
use NFS where appropriate and iSCSI where appropriate to the same tree
I suppose.  Too many options for us  :)

-Greg


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