[mythtv-users] Creative LVM configuration advice

[Albert James]

Hello MythTV community!
 
I am upgrading my storage server.  Currently 4x500G drives configured as (2 x SW RAID1) in a single VG and serving via NFS.  (For those that are interested, performance is fine even with 720p & 1080i with LiveTV and recording/viewing at same time).  This results in 1TB of storage which is simply not enough!  So I have two more 1TB drives on the way, and an external two bay USB/SATA enclosure.
 
I'm using this opportunity to rebuild the storage server to better meet my requirements.  I figured there are lots of people using LVM and/or RAID and wanted to poll the community to see what you're doing, and solicit feedback on my options.
 
For me, there are two types of media, "would rather not lose" (but willing to lose in a disk failure) and "can not lose" (i.e. must be redundant).  Data such as photos I need to be redundant, since this will likely be my only (on line) store.  DVD content I'm willing to lose, since I own and have the original media.  Music I'm also willing to lose for the same reason (although the files are generally small, so I'd put them on a redundant store if easier).  Recordings I'm struggling with, but leaning towards non-redundancy.  (If there is a must-keep program, I could always move (/archive?) it over to a redundant volume)
 
All this in mind, I need to create a storage architecture.  I'll have two large disks, four small disks, room for four internal drives, and two external (via USB).  I want to configure this such that Myth has optimal performance, but keep it as simple as possible (I believe creating too many RAIDs, VGs, etc. will limit versatility down the road).  The external device supports JBOD or dual drive mode only, no RAID.
 
Here is what I think my options are -- please provide feedback, criticisms, throw tomatoes, shoot holes, etc.
 
OPTION 1 -- I originally leaned towards creating a single VG with 6 PVs; using LV mirrors for the data that needs to be redundant, and specifying (I think during lvcreate) which PV(s) to create LV(s) on.  (I know I could do this with AIX LVM, and think I can with the Linux LVM2, but need to validate)  I would create a recordings LV of 1T and stripe it across the two 1T disks.  I would create mirrored LVs for photos and music and specify the USB disks (since those are slower).  Then I'd need to create a LV for DVD content, perhaps also 1T (though I'm not sure whether I'd stripe that or not, since I don't know whether DVD reads are more random access or streaming...streaming I would guess...)  (I don't know yet whether I'd LVM mirror the OS partitions, but I would like the box to stay up in a failure)
 
OPTION 2 -- There is another option I had considered using a SW mirror for the external 500G disks, HW mirror for the internal 500G disks, and a single VG.  Then specify which PV to create LVs on (i.e. photos/music on the external RAID1, OS files on the internal RAID1, recordings and DVDs on the 1T disks).
 
OPTION 3 -- This was an after thought...but since RAID5 is optimized for streaming, keep the 4 500G disks inside the machine and put the 2T disks in the enclosure.  I think a RAID5 4x500G array yields 1.5T.  Use LVM on that for OS, recordings and photos.  Use the external 1T disks for DVD content and music, again with LVM.  This would probably end up being two seperate VGs.
 
Questions:
     1.  Is anyone out there running a configuration like any of these?  Do you have any thoughts, lessons learnt, etc?
     2.  Can anyone comment on the feasability of any of the options?
          (or do you know a good how-to resource for LVM...the ones I've found via google search don't seem to go into performance details)
     3.  Do you think Myth, from a performance perspective, would prefer either option?
     4.  In option 1 or 2, would you stripe the DVD LV?
     5.  Are there any PE size considerations for myth?  (Obviously I'd like to go as large as possible)
 
Any advice or comments would be appreciated.
 
--A 


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