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BullCreek
March 22nd, 2010, 08:48 PM
I downloaded the alternate cd for 10.04 BETA because I assumed that the mythbuntu download being a "desktop" build didn't have support for mdadm in it. The mdadm part worked fine, but when I go to put a filesystem (any kind of filesystem) on the 7.5TB partition, it craps out. I filed a bug here:

http://bugs.launchpad.net/bugs/543838

In doing a little more reading, it strikes me that the bug may be with partman rather than the kernel. Anyone else run into this and know of a workaround?

ian dobson
March 22nd, 2010, 09:35 PM
Hi,

Looks as if the good old "fdisk/dos partition table" can't handle a partiton larger than 2Tb.

I have a 4Tb RAID5 array:-



Disk /dev/md0: 20.0 GB, 20012007424 bytes
2 heads, 4 sectors/track, 4885744 cylinders
Units = cylinders of 8 * 512 = 4096 bytes
Disk identifier: 0x00000000

Disk /dev/md0 doesn't contain a valid partition table

Disk /dev/md1: 3960.8 GB, 3960767250432 bytes
2 heads, 4 sectors/track, 966984192 cylinders
Units = cylinders of 8 * 512 = 4096 bytes
Disk identifier: 0x00000000

Disk /dev/md1 doesn't contain a valid partition table


I just formated the drive (md2) without creating a partition table. Maybe you can use partd with GUID partition table format (GPT) but I can't help you there.

Regards
Ian Dobson

BullCreek
March 22nd, 2010, 09:47 PM
Yes, I agree that GPT might work if I wasn't lazy and wanted to take the time to figure that out by trial and error - but what is puzzling is that this has not been a problem in prior releases (I have an intrepid box running a 2.9TB raid6 array and a karmic one running a 7.5TB array with no problems). Hopefully someone will chime in with answers...

ian dobson
March 23rd, 2010, 05:42 AM
So is your 7.5Tb array partitioned?

can you do a fdisk -l and post the results from the large array here.

Regards
Ian Dobson

ian dobson
March 23rd, 2010, 06:35 PM
Hi,

In afew days I'll be getting several 2Tb/4k sector WD drives for some tests. Although the end user doesn't run ubuntu I'll "test" them over the weekend on my ubuntu backed as a RAID array.

I'll try dos partitions/gpt partions with fdisk/gpartd and add my findings here.

Regards
Ian Dobson

BullCreek
March 23rd, 2010, 07:15 PM
Thanks for the comments. I think this is a problem with the alternate CD installer and not the kernel, as if I do "mkfs.ext4 /dev/md0" or "mkfs.xfs /dev/md0" on the command line it works fine and I can mount the resulting filesystem and use it.

I guess my setup is a little different than yours in that I'm not partitioning the mdadm block device per se - just using the whole device as a single partition which is also the way the alternate CD installer has done it traditionally. Hopefully someone will pick up the bug I filed and run with it.

At some point before too long, I'm probably going to switch my 750GB drives to 2TB or whatever is biggest at the time so I'd definitely be interested in hearing your results on the new 4k sector drives.

ian dobson
March 23rd, 2010, 08:53 PM
Hi,

You can format a block device (/dev/md0) without creating a partition, thats how I created my ext4 4Tb MythTV recordings drive.

You wanted to create a partition table on your 7Tb array, but the good old DOS compatible partition table can only support 2Tb partitions. Larger partitions can be created using gpartd/gpt partition format.

I do not think this is a bug (unless you want to open a bug report with MS for msdos 6.2), this is a limitation of the dos compatibility.

You said you have a "karmic one running a 7.5TB", please attach a fdisk -l if you want to prove me wrong.



Regards
Ian Dobson

BullCreek
March 23rd, 2010, 11:56 PM
I don't have access to the karmic machine right now, but here is an older intrepid machine with a 3TB /dev/md1 array with no partition table that is working fine - a block device is a block device is it not?

root@mythtv:~# df
Filesystem 1K-blocks Used Available Use% Mounted on
/dev/sdg1 11535344 7989936 2959440 73% /
tmpfs 1036156 0 1036156 0% /lib/init/rw
varrun 1036156 356 1035800 1% /var/run
varlock 1036156 0 1036156 0% /var/lock
udev 1036156 2872 1033284 1% /dev
tmpfs 1036156 0 1036156 0% /dev/shm
lrm 1036156 2204 1033952 1% /lib/modules/2.6.27-14-g
eneric/volatile
/dev/sdg6 84926264 73404672 11521592 87% /var/lib
/dev/md1 2930156544 2570752924 359403620 88% /var/lib/mythtv
root@mythtv:~# fdisk -l /dev/md1

Disk /dev/md1: 3000.6 GB, 3000614518784 bytes
2 heads, 4 sectors/track, 732571904 cylinders
Units = cylinders of 8 * 512 = 4096 bytes
Disk identifier: 0x00000000

Disk /dev/md1 doesn't contain a valid partition table
root@mythtv:~# uname -a
Linux mythtv 2.6.27-14-generic #1 SMP Tue Aug 18 16:25:45 UTC 2009 i686 GNU/Linux
root@mythtv:~#

ian dobson
March 24th, 2010, 06:26 AM
Hi,

I think partman tries to create a partition table on the block device, but as the block device is larger than 2Tb it fails.

Formatting a block device (without a partition table) is supported on linux no problems, other operating systems might not see it and think the drive is empty. To reduce the chance of a mixup I always partition the drives that end up in the array and tell mdadm to use the partitioned device (/dev/sda1 and not /dev/sda).

Regards
Ian Dobson

ian dobson
March 25th, 2010, 09:45 PM
Hi,

OK, I've just picked up 2 4K sector 2Tb drives. Using fdisk with the -u option I've created a partition that starts on sector 64 (4Kb boundry). I then created a RAID0 block device over the 2 drives and formated the block device with ext4.

I'm currently formatting/copying data over to the array, this takes a while to copy 2.5Tb :o

Regards
Ian Dobson