On 29/10/2010 15:18, Mathias Burén wrote:

Hi,

I've a few questions in relation to mdadm and performance. System
details follow below:

Intel Atom 330 @ 1.6Ghz (dualcore, HT), 4GB RAM

[...]

Question 1: I saw that in Linux 2.6.36 (perhaps earlier versions as
well) you have the kernel config option CONFIG_MULTICORE_RAID456. I
tried enabling it, booted to 2.6.36 from 2.6.35, and rebuilding of the
array continued where it left off before reboot. However, the
performance was abysmal.. around 16MB/s compared to 70MB/s without the
option turned on. Is this a bug, or is it because the Atom has no
grunt to speak of?

No, the performance of MULTICORE_RAID456 is abysmal on any CPU. It's an 
experimental implementation that doesn't work terribly well. If you're 
interested in developing, by all means help, but if not, turn it off.

Question 2: The array is now recovering since I've grown it to 6 from 4 devices:
$ cat /proc/mdstat
Personalities : [raid6] [raid5] [raid4]
md0 : active raid5 sdf1[0] sde1[5] sdg1[6] sdc1[3] sdd1[4] sdb1[1]
       5851054080 blocks super 1.2 level 5, 128k chunk, algorithm 2
[6/6] [UUUUUU]
       [===========>.........]  reshape = 57.7% (1126387328/1950351360)
finish=718.0min speed=19125K/sec

unused devices:<none>

Is there a way to speed it up? /proc/sys/dev/raid/speed_limit_min is
100000 (100k), /proc/sys/dev/raid/speed_limit_max is 1000000 (1000k).

No, that's probably about right on something as weak as an Atom. Let it run.

Question 3: Before I created this RAID5 array I did a quick RAID0 test
array just for fun, using 2 full devices (not partitions). Now I have
this:

[...]

Sorry, I don't know the answer to this. I suspect it's to do with 
superblock versions, but I don't know - I'm sorry that's not helpful.

Cheers,

John.

--
To unsubscribe from this list: send the line "unsubscribe linux-raid" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html