This page describes setting up RAID 1 (mirror drives) on the NSLU2 under Unsling6.8 Beta.(Possibly applies to 6.10 also). Documentation originally taken from the unslung5 documentation and altered appropriately. The process starts with a blank drive and an unslung drive and ends up with two mirrored drives containing all the data stored on the originally-unslung drive. This is achieved by creating a raid array with just the blank second drive at first, copying the entire contents of the unslung drive onto it and then hotadding the unslung drive to the raid array.
Diversion scripts have been written to start the raid array during the boot process and stop the array before shutdown. Unfortunately it is not possible to stop the array that contains the root filesystem during the shutdown process. This means that that array is marked as 'dirty' on shutdown and it will resync when restarted. Resyncing can take hours for a large partition and no other process can run while the resyncing is happening. To get around this problem this howto splits the root partition into a small partition containing the system files and a much larger partition to hold public files.
This howto uses custom partitions on the attached hardrives making it impossible to return to the normal Unslung setup without repartitioning the drives and wiping all data. (Of course you can transfer the data off the drives before re-partitioning).
I'm just curious about the use of mirrored swap partitions. I would basically set up swap in striped mode (Raid0) for performance. But if you take a look at http://linas.org/linux/Software-RAID/Software-RAID-8.html (Question 18) you'll see that you don't need to set up Raid0 for swap because the linux kernel is doing this automatically.
Note that the notes below have worked for me, however if you start with an unslung drive on DISK 1, the "unslung" drive will initially be /dev/sda (not /dev/sdb as described below). Thus, for this to work for me, I had to reverse the instructions (i.e. using /dev/sda where /dev/sdb was specified, and vice-versa).
Change Hard Drive Partitions
The standard NSLU2-formatted disk has three partitions: A 50MB swap partition, a 100MB config partition (mounted as /share/hdd/conf) and the rest of the disk as a data partition (mounted as /share/hdd/data). Unslung 6.8 also uses the data partition as the root filesystem. When the NSLU2 is switched off or reboots it will try to stop all the raid arrays. Any arrays that are not cleanly stopped will resync during the startup process. The resyncing process can take up to 10 hours for a 300GB harddrive and no other processes can run during that time. That would mean that your sytem is out of action for up to 10 hours everytime you reboot and to avoid this I split the data partition into a 1GB root partition and a 299GB data partition.
This howto mirrors all four partitions. I had thought that mirroring the swap partition could have a performance cost when writing to disk (and indeed it does) but I believe there are more read operations (where there is a performance gain) than write operations on swap space. The files in the conf partition are used by Samba and the passwd utility so the conf partition must be mirrored if mirroring the data partition.
In order for the RAID arrays to work on a reboot we also need to change the partition types from
#/opt/bin/busybox fdisk /dev/sdb
Be careful to use /dev/sdb, the repartitioning process wipes all existing data from the drive.
Then press '
Disk /dev/sdb: 300.0 GB, 300090728448 bytes 255 heads, 63 sectors/track, 36483 cylinders Units = cylinders of 16065 * 512 = 8225280 bytes Device Boot Start End Blocks Id System /dev/sdb1 1 36461 292872951 83 Linux /dev/sdb2 36462 36476 120487+ 83 Linux /dev/sdb3 36477 36483 56227+ 82 Linux swap
Use option 'd' to delete all three partitions
Now use option '
Now use option '
Device Boot Start End Blocks Id System /dev/sdb1 1 150 1204843+ fd Linux raid autodetect /dev/sdb2 151 165 120487+ fd Linux raid autodetect /dev/sdb3 166 172 56227+ fd Linux raid autodetect /dev/sdb4 173 36483 291668107+ fd Linux raid autodetect
The sizes of the first three partitions should match this table exactly, the size of the fourth partition will depend on the size of the hard drive. My hard drive is 300GB.
Now use '
If fdisk requests a reboot for the changes to the partition table to become effective, do so. After rebooting, re-enabling telnet and logging in, don't forget to install the kernel modules again:
# /sbin/insmod md.o # /sbin/insmod raid1.o
Create and Mount RAID arrays
Create one array for each partition (four in total). The '
# mknod /dev/md4 b 9 4 2>/dev/null # /opt/sbin/mdadm --create --level=1 --raid-devices=2 /dev/md4 /dev/sdb4 missing # /opt/sbin/mdadm --create --level=1 --raid-devices=2 /dev/md3 /dev/sdb3 missing # /opt/sbin/mdadm --create --level=1 --raid-devices=2 /dev/md2 /dev/sdb2 missing # /opt/sbin/mdadm --create --level=1 --raid-devices=2 /dev/md1 /dev/sdb1 missing
# cat /proc/mdstat Personalities : [raid1] read_ahead 1024 sectors md1 : active raid1 scsi/host0/bus0/target0/lun0/part1 1204736 blocks [2/1] [U_] md2 : active raid1 scsi/host0/bus0/target0/lun0/part2 120384 blocks [2/1] [U_] md3 : active raid1 scsi/host0/bus0/target0/lun0/part3 56128 blocks [2/1] [U_] md4 : active raid1 scsi/host0/bus0/target0/lun0/part4 291668032 blocks [2/1] [U_] unused devices: <none>
There are other monitor functions that you can play around with such as "
Now we create the file systems on each of the four partitions, starting with the swap partition:
# /sbin/mkswap /dev/md3 # /sbin/swapon /dev/md3
# /usr/bin/mke2fs -j /dev/md2 # /usr/bin/mke2fs -j /dev/md1 # /usr/bin/mke2fs -j /dev/md4
Mount the new partitions on the 'flash' directory temporarily. We will remount them to their rightful place (/share/hdd/data) on reboot.
# mount -t ext3 /dev/md2 /share/flash/conf # mount -t ext3 /dev/md1 /share/flash/data # mkdir /share/flash/data/public # chown admin.everyone /share/flash/data/public # chmod 775 /share/flash/data/public # mount -t ext3 /dev/md4 /share/flash/data/public
Copy entire file system to RAID partitions
This code was nabbed from the
Please note that the following instructions are different depending on which version of unslung you are running
The revised syntax here should work for all versions of unslung and circumvent the requirement to install a new version of cpio for 6.10
# cd /share/hdd/conf # /usr/bin/find ./ -mount -print0 | /usr/bin/cpio -p -0 -d -m -u /share/flash/conf # cd / # /usr/bin/find . -path './public' -prune -o -mount -print0 | /usr/bin/cpio -p -0 -d -m -u /share/flash/data # cd /public # /usr/bin/find ./ -mount -print0 | /usr/bin/cpio -p -0 -d -m -u /share/flash/data/public
Syntax specific to pre Unslung 6.8
Note: Problems under 6.10beta using the above calls. I simply used "ipkg install cpio" to ensure the current version was installed. It then created "/opt/bin/cpio-cpio". My modified script is below. - (purpleonyx)
Note: I got here "/usr/bin/find:No such file or directory" and "/usr/bin/cpio: No such file or directory" errors as in Unslung 6.8beta those programs are in /opt/bin instead. /opt/bin/find prints the following warning which, however, doesn't seem to affect the result: "/opt/bin/find: warning: you have specified the -mount option after a non-option argument -print0, but options are not positional (-mount affects tests specified before it as well as those specified after it). Please specify options before other arguments." (2007-11-15 danher)
[Edit 23 march 2009]
This is an alternative script i made that worked for me:
The slug can manage about 10 Mbytes/sec at most so this last command could take a long time if you have a lot of data. There might be a quicker way using the dd command but this way works for me. (I have found the dd command useful for files that are too large for the cp command e.g. DVD ISO files)
In Unslung 6.8 the root filesystem is mounted on one of the harddrives on reboot. The script that actually does the mounting is called '
with these lines:
and replace these lines:
with these 5 lines:
The diversion scripts can be found at HowTo.Raid1DiversionScripts6.
Ensure that the new mdadm file has execute permissions (i.e.
and linuxrc.raid should be in here too. Make sure linuxrc.raid is executeble by typing chmod 777 linuxrc.raid
Note: this did not work as described here because the current version of mdadm is 280812 Bytes big and thus does not fit in the available space on initrd. So you have to delete something to make space. mwester suggest deleting unneeded samba codepages in /etc/samba
(see also http://www.nabble.com/mdadm-size-and-raid1-on-unslung-6-t4506191.html) (2007-11-15 danher)
The diversion scripts can be found at HowTo.Raid1DiversionScripts6. Exact permissions of the diversion scripts don't seem to matter. This is a listing of my unslung directory:
Resyncing the RAID Arrays
At this stage we have a working RAID array containing just a single drive. The second drive is still unslung and you could still return to your original configuration. The next step is to add the unslung drive to the raid array to take it out of degraded mode.
This step in the process wipes all data from your original unslung drive. If you're not confident about doing that for any reason then just perform these steps on another blank drive and leave your unslung drive untouched. That way, in order to return to your original configuration you just have to replace the original linuxrc file and reboot with the unslung drive attached.
While still running the slug from the second drive, prepare the partitions on the unslung drive in exactly the same way as it was done for the second drive before:
Now the array can be prepared to use both disks:
The order is important here: The /dev/md4 aray will take hours to resync so you should do the other three first.
Yes, it really will take 569 minutes (almost 10 hours) to resync my two 300GB drives (2007-11-15 danher: my two 500GB drives took 865 minutes or 14.5h). For $70 you get 10MByte/sec throughput and that's it! While the disks are resyncing it's best not to touch the slug. I have found that if I try to perform any I/O tasks the speed of resyncing falls precipitiously and never rises back up so I just leave it alone (say, overnight) until it's finished. There are parameters that can be adjusted (Google for mdadm speed_limit_max) but i have found them to be ineffective.
This is also the reason why the resyncing is done on the standard Linksys filesystem rather than the unslung filesystem: The slug is constantly writing to
Once the resyncing has completed we create a mdadm.conf file, then stop the raid arrays, edit
# /bin/echo "DEVICE /dev/sd[ab]" > /unslung/mdadm.conf # /unslung/mdadm --detail --scan >> /unslung/mdadm.conf
Mount the new root filesystem and copy mdadm.conf into place:
# mount -t ext3 /dev/md1 /share/hdd/data # cp /unslung/mdadm.conf /share/hdd/data/opt/etc/mdadm.conf # umount /share/hdd/data
Stop the raid arrays:
# /unslung/mdadm --stop --scan --config=/unslung/mdadm.conf
Switch off the slug and switch it back on again, telnet/ssh in and run
Err... that's it! You should have a working raid 1 array.
Reboot with one drive attached failed: If you were getting
Return to original unslung configuration:
Slug doesn't reboot with no drives attached: This is probably caused by an error in the linuxrc script. To fix it you will need to flash the 5.5 firmware onto the slug again. No data should have been lost at this stage and you can still return to your original unslung configuration. This section will not work unless you were unslung on 5.x (or maybe 4.x at a pinch).
Failed Drive: Repeat the steps in this howto starting at "Resyncing the RAID arrays".
Power Loss: Raid 1 obviously won't help if you lose both drives simultaneously but unless you're very unlucky you shouldn't lose any data. The worst that might happen is that one of the disks will have to be replaced if the slug was performing an I/O operation on it when the power went.
After a power loss you must restart the slug with no drives attached and then repeat the steps in this howto starting at "Resyncing the RAID arrays". The reason that you cannot simply reboot is that all 4 raid arrays will try to resync and, because of the load on the CPU during startup, they will never finish the resync.
If you suspect that the slug was performing a disk read or write operation when you lost power then the disks might be corrupted. Read http://www.tldp.org/HOWTO/Software-RAID-0.4x-HOWTO-4.html and follow steps 1 to 3 of method 2 before repeating the steps in this howto starting at "Resyncing the RAID arrays". PS The
This leads to the obvious warning: Never switch the slug off while it is reading/writing to a raid array (Drive lights flashing).