[mythtv-users] limiting size of a storage group
Michael T. Dean
mtdean at thirdcontact.com
Tue Nov 24 00:52:00 UTC 2009
On 11/23/2009 07:25 PM, Gabe Rubin wrote:
> Is it possible to limit how big a storage group is? I am running out
> of room on my mythbox but have tons of room on my windows computer. I
> am considering creating a shared drive on the windows computer,
> mounting it on my windows box, and making that mount point a storage
> group to be recorded to. However, I want to limit the size so myth
> recordings don't overtake the computer. Is this possible?
> I see that there is a free space setting, but it appears that it
> allocates that much free space for each storage group, so it would
> affect the local storage as well. I suppose I could create a
> partition on the windows machine dedicated for this purpose, but would
> like to avoid that if possible.
First a bit of terminology so we're on the same page.
A storage group is simply a list of directories. It has no "size" other
than the number of directories listed in it. So, if I have a "Default"
storage group whose only directory entry is "/srv/mythtv/tv/recordings",
the "Default" storage group has a size of 1.
The directory specified in the storage group is a file system object
that exists within a file system. The directory can generally contain
other file system objects--including files and other directories.
However, the directory itself has no size. The file system on which it
exists has a size that specifies the amount of storage space provided by
the file system.
The same directory can be listed in multiple different storage groups.
Different directories on the same file system can be listed in the same
/or/ different storage groups. Different directories on different file
systems can be listed in the same /or/ different storage groups.
In other words, there is absolutely no correlation between storage
groups and directories or storage groups and file systems. A storage
group is just a list of directories (with a human-readable "logical" name).
OK, now that we're speaking the same language, let's get to your
The way to limit the amount of space made available to MythTV is through
file system and/or operating system limits. The easiest approach to put
limits on file system usage is the hard limit imposed by the file system
size itself. You may do this by partitioning the drive appropriately
and/or using tools such as LVM to allow you to create file systems of
the desired size.
There are other options such as quotas or other operating-system
constraints on disk usage.
As you figured out, the "Extra Disk Space" setting isn't appropriate.
It specifies a number of gigabytes of storage space that MythTV should
not use, but is global across /all/ file systems. Therefore, if you
have a 200GB file system and a 2TB file system which contain directories
specified in MythTV storage groups, the same "Extra Disk Space" will be
applied to both file systems. So, whereas you may really want MythTV to
reserve 250GB of disk space for use by other applications on the 2TB
file system, you certainly don't want Myth to reserve 250GB of disk
space for use by other applications on the 200GB file system (or, if you
do, you should not be specifying any directories on that file system in
your MythTV storage groups).
I'll leave it up to others to suggest whether to use partitioning or LVM
or quotas or other mechanisms to limit MythTV's usage of the file
system. Especially since you're planning to use a Windows-managed file
system for the storage, the options you have (other than partitioning)
are well outside my area of experience.
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