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To lvm or not to lvm
http://forum.linhes.org/viewtopic.php?f=6&t=17161		 Page 1 of 1
Author:  mythingpersons [ Thu Nov 01, 2007 8:21 pm ]
Post subject:  To lvm or not to lvm
Let me start by expressing thanks and appreciation to Cecil, Dale and all contributers to the forum and wiki (you know who you are) for >2 years of fun and challenge with knoppmyth and countless hours of timeshifted tv entertainment.

I have just had a catastrophic hardware failure and find myself burned by lvm, i.e. the os was installed on hda1 with /myth lvm'd over hda3, sda1 and sda2. Needless to say it was hda that gave up on me. (I know I would still be up for reinstallation if I hadn't had lvm but I imagine the content on sda and sdb would still be accessable)

Listening to the interview with a geek had me excited about the upcoming R6, especially the storage groups.

Now that I am replacing hda and am up for a clean install I am wondering if I should avoid lvm and just symbolic link sda1 to /myth/tv and sdb1 to /myth/video?

Or do I go straight for myth 0.21 using the upgrade script at http://mysettopbox.tv/phpBB2/viewtopic.php?t=11985

When the R6 comes around will the upgrade take pre existing 0.21 into account? Or to put it another way will there be a way to go from lvm to storage groups?

Thanks
Author:  slowtolearn [ Thu Nov 01, 2007 8:51 pm ]
Post subject:  Re: To lvm or not to lvm
mythingpersons wrote:
Listening to the interview with a geek had me excited about the upcoming R6, especially the storage groups.

Now that I am replacing hda and am up for a clean install I am wondering if I should avoid lvm and just symbolic link sda1 to /myth/tv and sdb1 to /myth/video?

Or do I go straight for myth 0.21 using the upgrade script at http://mysettopbox.tv/phpBB2/viewtopic.php?t=11985
That wouldn't be 0.21, that would be SVN. 0.21 hasn't been released yet - http://svn.mythtv.org/trac/roadmap

mythingpersons wrote:
When the R6 comes around will the upgrade take pre existing 0.21 into account? Or to put it another way will there be a way to go from lvm to storage groups?
Once you have drives in an LVM, you always have an LVM (not really, but the hoops you have to jump through to eliminate the LVM are far beyond the scope of an upgrade of KM). You would be able to copy your data to <somewhere> then setup the storage group(s) and copy your data back.

If you need one big filesystem then you either A) need a single drive that covers that amount of space, or B) use LVM. Having had a drive failure within an LVM myself I would *strongly* recommend a backup solution to mitigate the damages should a drive go belly-up. I built another system and use rsync to backup the media each night.

If you can cover the necessary space by utilizing multiple drives mounted into various areas (such as one for /myth/tv, another for /myth/video) then you reduce the possibility of losing all of your data, but you can't eliminate the risk.

Just one boy's opinion...
Author:  Liv2Cod [ Fri Nov 02, 2007 1:30 am ]
Post subject: 
I faced the same decision and I came to the same conclusion. In my case, the partitions are so large that backup is impractical. I have a 750G drive at /myth/tv for HDTV shows, another 750G drive at /myth/video for DVDs. Then I have a 400G drive for / and /myth and all those other incidental files.

If I lose my TV shows... oh well. I'll cry me a river (not). If I lose my DVD drive, no big deal. I actually own the DVDs I rip so I could rip them again. The Myth box is just a convenient DVD changer that keeps me from cluttering my living room with boxes of DVDs.

I was also an early adopter of LVM and I have since shied away from it because of the threat of losing the whole enchilada when a single disk fails. Let's face it -- it's not a matter of if the disk will fail, it's when.
Author:  mythingpersons [ Fri Nov 02, 2007 5:01 pm ]
Post subject: 
Liv2Cod,
That sounds like a plan, put /myth/tv and /myth/video on individual drives with / and /myth on the new hda.

cheers and thanks
Author:  Liv2Cod [ Sat Nov 03, 2007 2:55 am ]
Post subject: 
Another thing I like about this approach is that I can format the big drives as XFS and leave the / and /myth drive as ext3. I've had really excellent results with XFS on my HDTV shows and I can't imagine doing without it. When I delete a football game it just goes "poof" and all 30G bytes evaporates instantly. But it's easier to just let KnoppMyth install the root drive and leave it as ext3.
Author:  cahlfors [ Tue Nov 06, 2007 1:50 pm ]
Post subject: 
Quote:
I was also an early adopter of LVM and I have since shied away from it because of the threat of losing the whole enchilada when a single disk fails.

The data would still be on the intact disks. Just recreate an LVM and put the intact disks in it. However, you don't know what's lost and what isn't. Any given file is written to just one of the drives, but you don't know which. I believe there is a script somewhere which syncs the database with what's actually available on disk (which is only an issue with the recordings). Could possibly be used to salvage what's left if there is a backup of the db.

There is also another approach to the storage problem if you are getting serious: Either buy yourself a four+ disk NAS from Synology, Infrant/Netgear, Buffalo, etc and set it up as RAID5, or build your own storage server with your favorite distro, FreeNAS or similar. When things get big, I do think it's a good idea to separate the KM system from the storage system entirely, since the storage system rarely needs maintenance or upgrade work, but KM does. I mean, who doesn't want the latest features? :D

Cheers,
/Chris
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