[mythtv-users] Two-backends with two-frontends on one machine?
Michael T. Dean
mtdean at thirdcontact.com
Wed Jul 11 23:06:36 UTC 2007
On 07/11/2007 06:40 PM, Jay Mallar wrote:
> RAID will work against me with MythTV 0.21 and up??
Technically, having fewer filesystems than capture cards will work
against you. RAID encourages the creation of one large filesystem, so...
> 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.
That's what Storage Groups does for you. Just assign multiple
filesystems to the default storage group and use that storage group for
all recordings and the rest is magic. You /can/ go to the extent of
putting specific recordings on specific disks, but--like you--I don't
want to mess with that.
> 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.
The argument is actually that using one filesystem per recording (which
I've done by using one spindle/disk per filesystem) reduces
fragmentation and seek issues. Storage Groups allows the use of
multiple filesystems; therefore, storage groups can be used to reduce
> I guess your point is the less
> you use a disk, the less chance of it being fragmented,
Not at all. My point is that when writing 2 or more concurrent
recordings to the same filesystem there /will/ be constant fragmentation
of both of those recordings because Myth does not pre-allocate the
blocks required for the recording (because there's no way it could do so).
> but I think
> that's a red herring, at least with popular Linux file systems.
For which you've tested for years with files averaging 1 or 2 GB (for
SDTV) or 6GB (for HDTV) with ranges from maybe 1 - 20 GB and a usage
scenario as created by a PVR-type application? Normal
desktop/workstation filesystem usage is /nothing/ like MythTV filesystem
usage, and--last I checked--the mythfs filesystem wasn't available. (I
don't even know if LIMEFS is available, either, and it certainly isn't
as well-tested as general-purpose filesystems.)
Might want to search the list archives for fragmentation or defrag or
defragment or ...
And, I'll be willing to bet if you do have years of MythTV usage
experience, you only have one data point...
> yet to have a need, in all my years of Linux, to defrag a Linux disk.
And how many years of that experience are associated with PVR-type
> What about MythTV would make me want to start?
Prebuffering pauses, but technically, in the case I'm discussing, they
are an issue of playback that's due to disk/filesystem issues--not due
to MythTV. :)
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