[mythtv-users] WAY OT: Storage designs

David Scammell davescammell at gmail.com
Mon Aug 30 22:25:16 UTC 2010

> I have been looking at SCST (or the likes) and iSCSI targets versus NFS/CIFS...
> Has anyone implemented this and have performance data?  I am
> netbooting all of my FEs, so would need root to be on an iSCSI target
> as well as all of the laptops in the house for backup purposes..  I
> have used iSCSI in the past - just not as an in kernel software module
> - it outperformed NFS in my tests then, but that was prior to
> in-kernel nfs4, so I have no recent data.
> Regardless - I'm going to test it, but other *horror* or *praise*
> stories are very welcome.

Hi Greg,
SCST, never played with that, another tab to be opened in the browser
for that, ho-hum.
no performance figures, i'm sorry, in my tests about a couple of years
ago NFSv3 vs. iscsi, iscsi won hands down.
I'm my disto of choice (debian), root on iscsi was fiddly to achieve
but doable, I had (since retired) an intel i386 pxe booting an iscsi
rooted nvidia based frontend quite reliably. Also an alpha based
machine (not myth related as such), Since the acer revo came along as
a frontend, it is so quiet even with its internal harddrive there
seemed to be no reason to not use that for the root filesystem and
dispense with an iscsi root.

I use ocfs2 as the shared filesystem on the iSCSI volumes for Mythtv
storage. It works quite nicely but I would recommend using a
reasonably recent vendor kernel in your favorite distro, I have had
corruption from time to time, requiring fscks which were not
completely successful. I have not really looked hard into this,
presumably Oracle (the originator of this fs) made it stable enough
for their production use but the current (BE) debian kernel I'm using
2.6.30 still appears to have issues. Actually some of my issues could
be down to bad hardware, I did have a failing disk at one point.

I am uk based an have a backend and combined FE/BE (revo), recording
typically 4 DVB(-T) SD streams but have had 9 going at the same time.
gig lan with cheap switches, no jumbo frames. Myth has 1TB under
ocfs2/iSCSI. The storage was mostly situated on the MBE apart from a
small 60GB volume on the revo (also ocfs2/iSCSI) until last night when
the MBE storage was moved onto a debianised seagate dockstar iSCSI
server which appears to be holding up well. That move is to allow the
eventual removal of the harddrive from the MBE in order to reduce the
average temperature of that machine (its in the attic).

(OT Dockstar, appears to have an average iscsi throught of about
20MB's per disk.An initial tests of 2 disks looks promising; doubling
that. It does appears to spend a lot of processing power talking over
the USB bus. I am looking forward to being able to pvmove one of my
500GB volumes from one disk to another on the dockstar without the
myth machines being any the wiser, the iSCSI target software won't

iSCSI/ocfs2, generally has my thumbs up. More tricky to do than nfs
but learning stuff never hurt anyone, much :)


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