Taken for what it is, here's some recent experience I'm seeing (not a
precise explanation as you're asking for, which I'd like to know also).
Layout : near=2, far=1
Chunk Size : 512K
gtmp01,16G,,,125798,22,86157,17,,,337603,34,765.3,2,16,240,1,+++++,+++,237,1,241,1,+++++,+++,239,1
gtmp01,16G,,,129137,21,87074,17,,,336256,34,751.7,1,16,239,1,+++++,+++,238,1,240,1,+++++,+++,238,1
gtmp01,16G,,,125458,22,86293,17,,,338146,34,755.8,1,16,240,1,+++++,+++,237,1,240,1,+++++,+++,237,1
Layout : near=1, offset=2
Chunk Size : 512K
gtmp02,16G,,,141278,25,98789,20,,,297263,29,767.5,2,16,240,1,+++++,+++,238,1,240,1,+++++,+++,238,1
gtmp02,16G,,,143068,25,98469,20,,,316138,31,793.6,1,16,239,1,+++++,+++,237,1,239,1,+++++,+++,238,0
gtmp02,16G,,,143236,24,99234,20,,,313824,32,782.1,1,16,240,1,+++++,+++,237,1,240,1,+++++,+++,238,1
Here, testing with bonnie++, 14-drive RAID10 dual-multipath FC, 10K 146G
drives. RAID5 nets the same approximate read performance (sometimes
higher), with single-thread writes limited to 100MB/sec, and
concurrent-thread R/W access in the pits (obvious for RAID5).
mdadm 2.5.3
linux 2.6.18
xfs (mkfs.xfs -d su=512k,sw=3 -l logdev=/dev/sda1 -f /dev/md0)
Cheers,
/eli
martin f krafft wrote:
I am trying to compare the three RADI10 layouts with each other.
Assuming a simple 4 drive setup with 2 copies of each block,
I understand that a "near" layout makes RAID10 resemble RAID1+0
(although it's not 1+0).
I also understand that the "far" layout trades some read performance
for some write performance, so it's best for read-intensive
operations, like read-only file servers.
I don't really understand the "offset" layout. Am I right in
asserting that like "near" it keeps stripes together and thus
requires less seeking, but stores the blocks at different offsets
wrt the disks?
If A,B,C are data blocks, a,b their parts, and 1,2 denote their
copies, the following would be a classic RAID1+0 where 1,2 and 3,4
are RAID0 pairs combined into a RAID1:
hdd1 Aa1 Ba1 Ca1
hdd2 Ab1 Bb1 Cb1
hdd3 Aa2 Ba2 Ca2
hdd4 Ab2 Bb2 Cb2
How would this look with the three different layouts? I think "near"
is pretty much the same as above, but I can't figure out "far" and
"offset" from the md(4) manpage.
Also, what are their respective advantages and disadvantages?
Thanks,
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