Re: RAID10: near, far, offset -- which one?
On Thursday October 5, [EMAIL PROTECTED] 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. near=2 would be hdd1 Aa1 Ba1 Ca1 hdd2 Aa2 Ba2 Ca2 hdd3 Ab1 Bb1 Cb1 hdd4 Ab2 Bb2 Cb2 offset=2 would be hdd1 Aa1 Bb2 Ca1 Db2 hdd2 Ab1 Aa2 Cb1 Ca2 hdd3 Ba1 Ab2 Da1 Cb2 hdd4 Bb1 Ba2 Db1 Da2 far=2 would be hdd1 Aa1 Ca1 Bb2 Db2 hdd2 Ab1 Cb1 Aa2 Ca2 hdd3 Ba1 Da1 Ab2 Cb2 hdd4 Bb1 Db1 Ba2 Da2 Where the second set start half-way through the drives. The advantage of far= is that you can easily spread a long sequential read across the drives. The cost is more seeking for writes. offset= can possibly get similar benefits with large enough chunk size, though I haven't tried to understand all the implications of that layout. I added it simply because it is a supported layout in DDF and I am working towards DDF support. NeilBrown - To unsubscribe from this list: send the line unsubscribe linux-raid in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
RAID10: near, far, offset -- which one?
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, -- martin; (greetings from the heart of the sun.) \ echo mailto: !#^.*|tr * mailto:; [EMAIL PROTECTED] spamtraps: [EMAIL PROTECTED] a woman begins by resisting a man's advances and ends by blocking his retreat. -- oscar wilde signature.asc Description: Digital signature (GPG/PGP)
Re: RAID10: near, far, offset -- which one?
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, - To unsubscribe from this list: send the line unsubscribe linux-raid in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
