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LVM and root partition Disk Migration Suggestions NAS, SAN?
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Author:  jmacmythtv [ Sat Jan 31, 2009 9:02 am ]
Post subject:  LVM and root partition Disk Migration Suggestions NAS, SAN?
Hi everyone,

I am looking to remove the two oldest disks in my system and add one or two larger, new disks. (preventative maintenance).

The current setup:

1 250 GB drive with 2 partitions: a 5GB root partition, and 245GB in my LVM
1 250GB drive with 1 partition in LVM
1 500GB drive with 1 partition in LVM

The 2 250GB are 3+ years old. The 500 was added a couple of months ago. Disk IO is degrading and the noise from the disks has increased and is worrisome.

I would like to break the LVM (and start using storage groups), and put my root partition on a newer disk. I have not bought any new disks yet.

Another option that I have toyed around with is some sort of SAN or NAS setup to a separate machine (using iscsi for the SAN).

Looking for general comments on the migration approach and any experiences using NAS/SAN for /myth.

tks!
Author:  graysky [ Sat Jan 31, 2009 10:32 am ]
Post subject: 
I wouldn't mess with a NAS at all unless you have the $$$ to buy or build one. My advice would be to get a new, single drive, install R5.5, restore backups, and simply rsync over your /myth partition. See that thread for details, but basically:

1) run mythbackup on your existing system and copy the /myth/backup somewhere
2) unplug all drives of the existing system, plug in the new drive and install R5.5 to the new drive
3) copy over the backups to the new drive and restore them
4) rsync the contents of /myth from the old drives to the new drive

If you're current setup is only 750 GB, you might not even need storage groups assuming you go for a big one drive solution. You have MANY options for new drives. Western digital has a 2.0 TB drive now (WD20EADS). Newegg has them in stock for $300 shipped but you'll be paying a premium for that extra 0.5 TB over the existing 1.5 TB drives. You have the choice of many different options in 750 GB, 1.0 TB, and 1.5 TB drives. Using the price on the WD 2 gig and the current (31-jan-09) pricing on the 11th gen, 32 MB cache Seagate drives (7200.11 series), the sweet-spot in the curve seems to be 1.5 TB:

2.0 GB drive for $300 = 6.7 GB/dollar
1.5 GB drive for $130 = 11.5 GB/dollar
1.0 GB drive for $104 = 9.6 GB/dollar
750 GB drive for $80 = 9.4 GB/dollar

If you can wait, I would say wait. Why? The 12th gen Seagate drives are due out in a few weeks are promise less power consumption, less heat, and more performance. If your concerned about data loss in your current drive set due to clicking, do NOT wait and backup critical data now.
Author:  akulcsar [ Sat Jan 31, 2009 4:03 pm ]
Post subject: 
I mostly second graysky's comments. In my original setup, /myth/tv always was a separate disk, so I could wipe the operating system disk with no fear of affecting my recordings. It wasted a bit of disk space, but my OS disk always is the smallest available (presently either 40 GB or 80 GB). I am a staunch supporter of placing your recordings onto a separate disk if you have the means, and with storage groups doing so is easier than ever.

My current setup does use iSCSI for /myth/tv, so I can vouch for the fact that it works (though you have to do a bit of tinkering in R5.5; I have posted elsewhere regarding that). I do not, however, advise it unless your setup warrants such extremes (or, in my case, you need to test some new equipment :D ).

NAS really is not a great solution except in really specific circumstances (and, to be honest, I cannot come up with any good examples). Instead, I would put the additional cost of a NAS system toward an additional disk or a larger disk and simply enable NFS and/or samba on the KnoppMyth box.
Author:  jmacmythtv [ Sun Feb 01, 2009 1:40 pm ]
Post subject: 
Thanks for the responses guys! OK, for the moment, NAS/SAN is out (I really just liked the idea expanding my hardware to a large server in the basement.)

I do like the idea (and was already leaning towards) having a separate disk for the OS.

Regarding the transfer process: I think that I am going to have to have the new drive(s) and the old ones on the same system because I don't have another computer or motherboard where I can plug in all 3 drive that make up the LVM group. My motherboard only has 4 ports ...

So here is the plan:

Add 1 new drive that is large enough to hold my /myth (>=1TB)
Copy/rsync over the data (3 drive LVM > new drive)
Change /etc/fstab so the /myth directory is mounted on the new drive
Backup the system to the new drive (watch that I have enough space)
Remove the LVM disks (3)
Add my new OS disk (and potentially another new disk)
Install to the new disk
Restore from the Backup
Add other disks as storage groups instead of LVM members

Does this make sense?

tks!
Author:  graysky [ Sun Feb 01, 2009 2:55 pm ]
Post subject: 
jmacmythtv wrote:
I do like the idea (and was already leaning towards) having a separate disk for the OS.


You could, but I don't see the point. This is why you partition the large disk. In fact, R5.5 will do this for you:

6 gig / partition (/dev/sda1)
2 gig swap partition (/dev/sda2)
x gig /myth (/dev/sda3) where x = the rest of the drive

When you reinstall or upgrade, the /myth partition is left untouched. I don't see what advantage a dedicated HDD offers for /myth or whatever /data partition you use :?:

jmacmythtv wrote:
Add 1 new drive that is large enough to hold my /myth (>=1TB)
Copy/rsync over the data (3 drive LVM > new drive)
Change /etc/fstab so the /myth directory is mounted on the new drive
Backup the system to the new drive (watch that I have enough space)
Remove the LVM disks (3)
Add my new OS disk (and potentially another new disk)
Install to the new disk
Restore from the Backup
Add other disks as storage groups instead of LVM members

Does this make sense?


Well, why not just keep your boot HDD and set your new large drive up in the /etc/fstab to /myth - this way you'll avoid a reinstall of KM all together so long as you keep the old HDD that you're booting off at this point. Again though, I just don't see the advantage of a two drive system (250 gig + 1.0 or 1.5 TB).

You don't need to reply justifying your decision. It's your hardware after all and this is just one man's opinion :)
Author:  jmacmythtv [ Sun Feb 01, 2009 4:26 pm ]
Post subject: 
Hi Graysky!

Thanks for the comments.

I have no info to back this up, but my hypothesis is that a drive that is constantly in I/O (recordings in /myth) will not last as long vs. a disk holding the OS files ... which is occasionally writing to var, reading some configs from etc, etc...

WRT your other suggestion of just relocating /myth - I would do that but I am worried about the old 250GB drives dying on me, so I definitely want to boot from a newer disk.

tks!
Author:  graysky [ Sun Feb 01, 2009 5:19 pm ]
Post subject: 
jmacmythtv wrote:
Hi Graysky!

Thanks for the comments.

I have no info to back this up, but my hypothesis is that a drive that is constantly in I/O (recordings in /myth) will not last as long vs. a disk holding the OS files ... which is occasionally writing to var, reading some configs from etc, etc...

WRT your other suggestion of just relocating /myth - I would do that but I am worried about the old 250GB drives dying on me, so I definitely want to boot from a newer disk.

tks!


I don't think a modern drive will be I/O limited in any measurable way by keeping a live system on it and your /myth partition. Keep it simple with a single drive :)
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