On Fri Dec 21, 2012, Thomas Fjellstrom wrote:
> I'm setting up a little home NAS here, and I've been thinking about using
> bcache to speed up the random access bits on the "big" raid6 array (7x2TB).
>
> How does one get started using bcache (custom patched kernel?), and what is
> the recommended setup for use with mdraid? I remember reading ages ago that
> it was recommended that each component device was attached directly to the
> cache, and then mdraid put on top, but a quick google suggests putting the
> cache on top of the raid instead.
>
> Also, is it possible to add a cache to an existing volume yet? I have a
> smaller array (7x1TB) that I wouldn't mind adding the cache layer to.
I just tried a basic setup with the cache ontop of the raid6. I ran a quick
iozone test with the default debian sid (3.2.35) kernel, the bcache (3.2.28)
kernel without bcache enabled, and with bcache enabled (See below).
Here's a little information:
system info:
Intel S1200KP Motherboard
Intel Core i3 2120 CPU
16GB DDR3 1333 ECC
IBM M1015 in IT mode
7 x 2TB Seagate Barracuda HDDs
1 x 240 GB Samsung 470 SSD
kernel: fresh git checkout of the bcache repo, 3.2.28
Raid Info:
/dev/md0:
Version : 1.2
Creation Time : Sat Dec 22 03:38:05 2012
Raid Level : raid6
Array Size : 9766914560 (9314.46 GiB 10001.32 GB)
Used Dev Size : 1953382912 (1862.89 GiB 2000.26 GB)
Raid Devices : 7
Total Devices : 7
Persistence : Superblock is persistent
Update Time : Mon Dec 24 00:22:28 2012
State : clean
Active Devices : 7
Working Devices : 7
Failed Devices : 0
Spare Devices : 0
Layout : left-symmetric
Chunk Size : 512K
Name : mrbig:0 (local to host mrbig)
UUID : 547c30d1:3af4b2ec:14712d0b:88e4337a
Events : 10591
Number Major Minor RaidDevice State
0 8 0 0 active sync /dev/sda
1 8 16 1 active sync /dev/sdb
2 8 32 2 active sync /dev/sdc
3 8 48 3 active sync /dev/sdd
4 8 80 4 active sync /dev/sdf
5 8 96 5 active sync /dev/sdg
6 8 112 6 active sync /dev/sdh
Fs info:
root@mrbig:~/build/bcache-tools# xfs_info /dev/bcache0
meta-data=/dev/bcache0 isize=256 agcount=10, agsize=268435328 blks
= sectsz=512 attr=2
data = bsize=4096 blocks=2441728638, imaxpct=5
= sunit=128 swidth=640 blks
naming =version 2 bsize=4096 ascii-ci=0
log =internal bsize=4096 blocks=521728, version=2
= sectsz=512 sunit=8 blks, lazy-count=1
realtime =none extsz=4096 blocks=0, rtextents=0
iozone -a -s 32G -r 8M
random random bkwd record stride
KB reclen write rewrite read reread read write read rewrite read fwrite frewrite fread freread
w/o cache (debian kernel 3.2.35-1)
33554432 8192 212507 210382 630327 630852 372807 161710 388319 4922757 617347 210642 217122 717279 716150
w/ cache (bcache git kernel 3.2.28):
33554432 8192 248376 231717 268560 269966 123718 132210 148030 4888983 152240 230099 238223 276254 282441
w/o cache (bcache git kernel 3.2.28):
33554432 8192 277607 259159 709837 702192 399889 151629 399779 4846688 655210 251297 245953 783930 778595
Note: I disabled the cache before the last test, unregistered the device and
"stop"ed the cache. I also changed the config slightly for the bcache kernel,
I started out with the debian config, and then switched the preemption option
to server, which may be the reason for the performance difference between the
two non cached tests.
I probably messed up the setup somehow. If anyone has some tips or suggestions
I'd appreciate some input.
--
Thomas Fjellstrom
thomas@xxxxxxxxxxxxx
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