[mythtv-users] Storage groups to solve I/O wait

Taco Mel taco_mel at yahoo.com
Tue Aug 21 01:27:57 UTC 2007

Today I experienced, for the first time, hesitation
while I was watching a show being recorded in HDTV. 
My setup for the back end is MythTV 0.21 (r14051),
pcHDTV 5500, Hauppauge PVR-500, and 3Ware 9500S on an
old Dell Precision 530.  This is a single PCI bus. 
The pcHDTV was recording the aforementioned HD show,
the Hauppauge was recording something else, and all
recordings access the disk via the 9500S (disks are in
a true hardware RAID-5 and file system is xfs).  I was
"chase playing" the HD recording.

The iowait was around 60-80% for each CPU according to
"top".  My guess is that I saturated the PCI bus.

Trying to use the hardware I have now (with an eye to
possibly upgrading in the future), I was wondering if
storage groups might help me here.  Currently my IDE
(dual channel ATA-100) are set up with the system disk
as a master on one channel and the DVD as the master
on the second channel.  My idea is this: put another
IDE drive in there (or maybe 2 with RAID-0), and set
up MythTV so that recordings are sent there.  Think of
this as a "staging area" of sorts.  Then, during a
period of low activity (e.g. middle of the night) a
process will come along and copy all of the recordings
from the IDE drive onto the SATA RAID array.  My goal
is that everything gets protected by RAID, although
losing one day's worth of recordings would not be the
end of the world.

My questions, therefore:

1. Is there a better solution (other than purchasing
faster hardware) - i.e., am I making this too

2. Is there any misunderstanding in the capabilities
of storage groups that would make my idea unworkable
right from the outset?  Is my idea just plain stupid
for any reason?

3. Is it better to configure them as two separate
drives (mounted in two separate directories with equal
priority) or as a software RAID-0?

I've got some old IDE drives sitting around and would
not mind spending a little money to get drives with a
larger cache if that might help.  Thanks in advance
for any advice.

Sick sense of humor? Visit Yahoo! TV's 
Comedy with an Edge to see what's on, when. 

More information about the mythtv-users mailing list