Speeding up chunk size change?

[Steven Haigh <netwiz@xxxxxxxxx>]

Hi all,

I just wanted to run this past a few folk here as I want to make sure 
I'm doing it the Right Way(tm).

I've decided to experiment with using a 128Kb chunk size on my RAID6 
instead of a 64kb chunk. To prepare for this, I removed the internal 
bitmap, then started the reshape via:

# mdadm --grow /dev/md2 --chunk=128K --backup-file=/md2-backup-file

This is slowly going on, however it will take much longer than I expected:

md2 : active raid6 sdf[6] sde[5] sdb[4] sda[3]
      1953520896 blocks super 1.2 level 6, 64k chunk, algorithm 2 [4/4] 
[UUUU]
      [>....................]  reshape =  0.6% (6649600/976760448) 
finish=2576.1min speed=6275K/sec

I set a few 'optimisations' that I believe should help:
## Tweak the RAIDs
blockdev --setra 8192 /dev/sd[abcdefg]
blockdev --setra 8192 /dev/md0
blockdev --setra 8192 /dev/md1
blockdev --setra 16384 /dev/md2
echo 16384 > /sys/block/md2/md/stripe_cache_size

for i in sda sdb sdc sdd sde sdf; do
        echo "Setting options for $i"
        echo 256 > /sys/block/$i/queue/nr_requests
        echo 4096 > /sys/block/$i/queue/read_ahead_kb
        echo 1 > /sys/block/$i/device/queue_depth
        echo deadline > /sys/block/$i/queue/scheduler
done

Just wondering if anyone knows of any possible way to speed up the 
reshape a little, or if (like I suspect) it will take ~2 days to 
complete the reshape.

--
Steven Haigh

Email: netwiz@xxxxxxxxx
Web: http://www.crc.id.au
Phone: (03) 9001 6090 - 0412 935 897
Fax: (03) 8338 0299

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