samworm
Posts: 3
Joined: Wed Nov 28, 2012 11:55 am

Lack of RAID1 and RAID10 in 3.2.27

Wed Nov 28, 2012 12:31 pm

Code: Select all

[email protected] ~ $ ls /lib/modules/3.2.27+/kernel/drivers/md/
dm-crypt.ko  dm-log.ko            dm-mirror.ko  dm-raid.ko         dm-snapshot.ko  md-mod.ko  raid456.ko
dm-delay.ko  dm-log-userspace.ko  dm-mod.ko     dm-region-hash.ko  dm-zero.ko      raid1.ko
I appreciate that people get cross about the use of RAID on the pi, it's CPU and USB based IO are poor performance fits, but set that aside for a moment.

I'm creating a sandbox environment that loosely mirrors the configurations of servers I use. These servers are running RAID10 on sets of SATA disks. Failures of RAID sets (and practicing the recoveries thereof) can easily be modeled on the pi using £3 USB flash drives in a hub. But the lack of a RAID10 module confuses me. I can presumably compile one from the sources, but I'm curious - is there a reason the RAID modules aren't more comprehensive? Or is it just left out because the maintainers don't see the need?

Thanks,

--
Sam

dom
Raspberry Pi Engineer & Forum Moderator
Raspberry Pi Engineer & Forum Moderator
Posts: 5312
Joined: Wed Aug 17, 2011 7:41 pm
Location: Cambridge

Re: Lack of RAID1 and RAID10 in 3.2.27

Wed Nov 28, 2012 1:45 pm

Looks like the "next" firmware tree includes raid10.ko.
http://www.raspberrypi.org/phpBB3/viewt ... 25#p222362

If kernel moduels are desired then create a github issue and list the .config options you would like added (ideally after testing they work correctly on the Pi), and they'll probably be added.

samworm
Posts: 3
Joined: Wed Nov 28, 2012 11:55 am

Re: Lack of RAID1 and RAID10 in 3.2.27

Wed Nov 28, 2012 6:07 pm

Thank you Dom. I tried the upgrade you suggested and the RAID10 module seems to work correctly. Syncing the MD device is pretty slow but sequential reads are fast, its actually a very usable setup.

CPU utilization wasn't high, although I wasn't really monitoring that, and reads from a file on an EXT4 file-system compared well to reads from the raw flash devices.

Code: Select all

Average read from the drives ~21MB/s, average read from the RAID10 ~33MB/s.

/dev/sda
4096+0 records in
4096+0 records out
4294967296 bytes (4.3 GB) copied, 202.988 s, 21.2 MB/s
/dev/sdb
4096+0 records in
4096+0 records out
4294967296 bytes (4.3 GB) copied, 200.421 s, 21.4 MB/s
/mnt/Z
4096+0 records in
4096+0 records out
4294967296 bytes (4.3 GB) copied, 130.403 s, 32.9 MB/s
/dev/sda
4096+0 records in
4096+0 records out
4294967296 bytes (4.3 GB) copied, 207.551 s, 20.7 MB/s
/dev/sdb
4096+0 records in
4096+0 records out
4294967296 bytes (4.3 GB) copied, 201.282 s, 21.3 MB/s
/mnt/Z
4096+0 records in
4096+0 records out
4294967296 bytes (4.3 GB) copied, 129.417 s, 33.2 MB/s
/dev/sda
4096+0 records in
4096+0 records out
4294967296 bytes (4.3 GB) copied, 203.634 s, 21.1 MB/s
/dev/sdb
4096+0 records in
4096+0 records out
4294967296 bytes (4.3 GB) copied, 201.739 s, 21.3 MB/s
/mnt/Z
4096+0 records in
4096+0 records out
4294967296 bytes (4.3 GB) copied, 129.051 s, 33.3 MB/s


Wendo
Posts: 142
Joined: Sun Jun 10, 2012 8:27 pm

Re: Lack of RAID1 and RAID10 in 3.2.27

Sat Dec 01, 2012 4:01 am

The CPU power required to do mirroring and striping is so low you shouldn't notice it on the Pi.

RAID5 or RAID6 would probably have a noticeable affect though

Return to “Raspbian”