RAID (part 2)

I've been meaning to write about my RAID setup for a while. In October I found a deal for $90 300 gig SATA drives so I decided to go ahead and create my RAID with just two disks using RAID 1 (mirrored). This allowed me to get started on the processes of ripping all of my CDs to flac.

I decided to use mdadm instead of raidtools since it's supposedly easier to use and will probably have more support than the older raidtools.

I first created the RAID volume as /dev/md0

% sudo /sbin/mdadm --create --verbose /dev/md0 --level=1 --raid-devices=2 /dev/sda1 /dev/sdb1
mdadm: size set to 293049600K
mdadm: array /dev/md0 started.

Then I scanned the volume to see that it was actually there

% sudo /sbin/mdadm --detail --scan
ARRAY /dev/md0 level=raid1 num-devices=2 UUID=dde6d2cc:f2446c0b:f408b868:d1440f9a
devices=/dev/sda1,/dev/sdb1

Then I checked out /proc/mdstat to see what was going on. It was building the volume

% cat /proc/mdstat
Personalities : [raid1]
md0 : active raid1 sdb1[1] sda1[0]
 293049600 blocks [2/2] [UU]
 [==>..................]  resync = 14.8% (43617664/293049600) finish=65.3min speed=63584K/sec

Then I created a filesystem on that volume

% sudo /sbin/mkfs.ext3 /dev/md0
mke2fs 1.36 (05-Feb-2005)
Filesystem label=
OS type: Linux
Block size=4096 (log=2)
Fragment size=4096 (log=2)
36634624 inodes, 73262400 blocks
3663120 blocks (5.00%) reserved for the super user
First data block=0
Maximum filesystem blocks=75497472
2236 block groups
32768 blocks per group, 32768 fragments per group
16384 inodes per group
Superblock backups stored on blocks:
    32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632, 2654208,
    4096000, 7962624, 11239424, 20480000, 23887872, 71663616

Writing inode tables:  689/2236

So now it was there and working. I transfered a few gigabytes of data to the new filesystem and as it was copying I decided to test the failure case

% cat /proc/mdstat
Personalities : [raid1]
md0 : active raid1 sdb1[1] sda1[0]
   293049600 blocks [2/2] [UU]

unused devices: 

% sudo /sbin/mdadm --manage --set-faulty /dev/md0 /dev/sda1
mdadm: set /dev/sda1 faulty in /dev/md0

% cat /proc/mdstat
Personalities : [raid1]
md0 : active raid1 sdb1[1] sda1[2](F)
   293049600 blocks [2/1] [_U]

unused devices:

So the RAID is now in a failure state. As you can see above, only one out of two disks is working properly. So I pretended to remove a disk and add a new one with these commands

% sudo /sbin/mdadm /dev/md0 --remove /dev/sda1

% sudo /sbin/mdadm /dev/md0 --add /dev/sda1

% cat /proc/mdstat
Personalities : [raid1]
md0 : active raid1 sda1[2] sdb1[1]
    293049600 blocks [2/1] [_U]
    [>....................]  recovery =  1.6% (4721792/293049600) finish=72.9min speed=65906K/sec
unused devices:

I haven't yet figured out how to get this all to come together after a reboot so currently I have to run these commands after a reboot to bring everything back

% sudo /sbin/mdadm --assemble /dev/md0
% sudo mount /dev/md0 /raid0

Terra Pass

I just found out about a really cool company called Terra Pass that sells pollution credits to car owners. The CEO of the company jokes that all he does is sell $50 bumper stickers. The idea is that your car is pollution neutral if you stop a big business from polluting the equivalent amount CO2 as your car. Fortunately, there's a market-based approach to reducing pollution that allows companies that pollute less to sell credits to companies that pollute more. So there's an incentive to pollute less. The economist talks about this all the time. I think it's a great idea. I've already ordered two bumper stickers, one for the Jetta and one for the Volvo. So far most of the people who've bought these 'passes' are hybrid and small car owners. But hopefully more people who own SUVs and gas guzzling sports cars do the same.