[mythtv-users] Two-backends with two-frontends on one machine?

Jay Mallar surfing at jaymallar.com
Wed Jul 11 22:40:24 UTC 2007

On 7/11/07, billymacdonald at gmail wrote:

 > Michael T. Dean <mtdean[at]thirdcontact.com> wrote:
 > On 7/11/07, Michael T. Dean <mtdean[at]thirdcontact.com> wrote:
 > > On 07/11/2007 11:27 AM, Steven Adeff wrote:
 > > > 1) RAID 1 seems like overkill, why not go with RAID5? I've got a 6
 > > > drive RAID 5 device that keeps up with my 4 HD tuner backend with two
 > > > HD capable frontends no problem.
 > >
 > > And, in the future (i.e. 0.21 and up), RAID may in fact work against
 > > you. With Storage Groups, you can set up your system to write each
 > > recording to a separate disk (provided enough disks), thereby
 > > significantly reducing fragmentation and seek issues. I have 4 HDTV
 > > capture cards and more drives than capture cards and have configured
 > > Myth so that it will only write two shows to the same disk if 
that's the
 > > only way to record the show (i.e. if all the other disks are full).
 > > After using it this way for some time, I can say I'll never use a
 > > multiple-disk (RAID or LVM with multiple physical volumes) 
 > > with Myth again.
 > RAID 1&5 provide redundancy that I don't think your solutions
 > addresses. Your solution seems to be solving more of a problem that
 > isn't there IMO. I have 4 HDtuners, and 3 pvr250's. All 7 tuners can
 > record to my LVM volume (not striped, 3 disks) and I can play back an
 > HD recording at the same time. And these are cheap IDE drives that I
 > got on sale at Best Buy. Now being able to store recordings in more
 > than one location does provide flexibility which I believe is a good
 > thing. But I'm not sure it's really needed for performance.

RAID will work against me with MythTV 0.21 and up??  That seems a bit 
bizarre.  I see your point of using Storage groups to assign recordings 
to different disks, but in my mind, I don't have to want to mess with 
which tuners use which disks.  I want to set up a RAID 1 mirror (or 
several) and link them via LVM so MythTV sees one partition  (From what 
I can tell, LVM is a bit more flexible than Storage Groups.)

I'm not sure I buy the argument that using Storage Groups significantly 
reduces fragmentation and seek issues.  I guess your point is the less 
you use a disk, the less chance of it being fragmented, but I think 
that's a red herring, at least with popular Linux file systems.  I've 
yet to have a need, in all my years of Linux, to defrag a Linux disk.  
What about MythTV would make me want to start?

Your machine interests me tho - 4 HD, 3 SD tuners are putting out around 
35MB/s of data by themselves.  Nice.  And you're telling me you can 
actually use all those tuners, plus decode and watch HD streams, on the 
same machine, without any artifacts?  Do you channel skip?   What kind 
of hardware are you using (MB, CPU, tuners in particular)?


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