Re: Confusion with setting up new RAID6 with mdadm

[Zoltan Szecsei <zoltans@geograph.co.za>]

Hi,
One last quick question:

Neil Brown <neilb@suse.de> wrote:
> Depending on which version of mdadm you are using, the default chunk size
> will be 64K or 512K.  I would recommend using 512K even if you have an older
> mdadm.  64K appears to be too small for modern hardware, particularly if you
> are storing large files.
>
> For raid6 with the current implementation it is safe to use "--assume-clean"
> to avoid the long recovery time.  It is certainly safe to use that if you
> want to build a test array, do some performance measurement, and then scrap
> it and try again.  If some time later you want to be sure that the array is
> entirely in sync you can
>    echo repair>  /sys/block/md0/md/sync_action
> and wait a while.
>    
****************************************************
I have compiled the following mdadm on my Ubuntu 64 bit 10.04 Desktop 
system:
root@gs0:/home/geograph# uname -a
Linux gs0 2.6.32-25-generic #45-Ubuntu SMP Sat Oct 16 19:52:42 UTC 2010 
x86_64 GNU/Linux
root@gs0:/home/geograph# mdadm -V
mdadm - v3.1.4 - 31st August 2010
root@gs0:/home/geograph#

****************************************************
I have deleted the partitions on all 8 drives, and done a mdadm -Ss

root@gs0:/home/geograph# fdisk -lu

Disk /dev/sda: 2000.4 GB, 2000398934016 bytes
255 heads, 63 sectors/track, 243201 cylinders, total 3907029168 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00000000

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

Disk /dev/sdb: 2000.4 GB, 2000398934016 bytes

******************************************************
Based on the above "assume-clean" comment, plus all the help you guys 
have offered, I have just run:
mdadm --create /dev/md0 --metadata=1.2 --auto=md --assume-clean 
--bitmap=internal --bitmap-chunk=131072 --chunk=512 --level=6 
--raid-devices=8 /dev/sd[abcdefgh]

It took a nano-second to complete!

The man-pages for assume-clean say that "the array pre-existed". Surely 
as I have erased the HDs, and now have no partitions on them, this is 
not true?
Do I need to re-run the above mdadm command, or is it safe to proceed 
with LVM then mkfs ext4?

Thanks for all,
Zoltan

******************************************************
root@gs0:/home/geograph# mdadm -E /dev/md0
mdadm: No md superblock detected on /dev/md0.



root@gs0:/home/geograph# ls -la /dev/md*
brw-rw---- 1 root disk 9, 0 2010-11-15 19:53 /dev/md0
/dev/md:
total 0
drwxr-xr-x  2 root root   60 2010-11-15 19:53 .
drwxr-xr-x 19 root root 4260 2010-11-15 19:53 ..
lrwxrwxrwx  1 root root    6 2010-11-15 19:53 0 -> ../md0


root@gs0:/home/geograph# cat /proc/mdstat
Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] 
[raid4] [raid10]
md0 : active raid6 sdc[2] sdf[5] sdh[7] sdd[3] sdb[1] sdg[6] sda[0] sde[4]
       11721077760 blocks super 1.2 level 6, 512k chunk, algorithm 2 
[8/8] [UUUUUUUU]
       bitmap: 0/8 pages [0KB], 131072KB chunk

unused devices: <none>




*******************************************************












-- 

===========================================
Zoltan Szecsei PrGISc [PGP0031]
Geograph (Pty) Ltd.
P.O. Box 7, Muizenberg 7950, South Africa.

65 Main Road, Muizenberg 7945
Western Cape, South Africa.

34° 6'16.35"S 18°28'5.62"E

Tel: +27-21-7884897  Mobile: +27-83-6004028
Fax: +27-86-6115323     www.geograph.co.za
===========================================



-----
No virus found in this message.
Checked by AVG - www.avg.com
Version: 10.0.1153 / Virus Database: 424/3258 - Release Date: 11/15/10

--
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