On Sat, 25 May 2013 18:32:59 -0500 Stan Hoeppner <[email protected]> wrote:
Hi Stan, > > May be I am doing something wrong. > > Yes, you are. You're using only 2 disk drives. The md/RAID10 module > with two drives will perform nearly identical to RAID1. > > Adding insult to injury you are using 6GB partitions in your testing > setup. The "layouts" of md/RAID10 are only of benefit when you use the > entire disk capacity, or a very large portion of it. These layouts > obtain some advantage be changing the behavior of the disk head and thus > read latency. With a 6GB partition on a 1/2TB disk drive, the heads > will never travel outside of a single track. > OK. Thank's for your mail and sorry to make you loosing your time reading mine. One precision: english is NOT my mother tongue. It is difficult for me to know if you are cool or if you are kidding me. So, apparently, I have to read a lot of doc'. Because launching a massive read on the same devices did not give the same result when I took a look at <iostat -k 3> output: direct read on /dev/sdc5 Device: tps kB_read/s kB_wrtn/s kB_read kB_wrtn sdc 9,54 4347,36 34,94 16514421 132725 sdc 0,00 0,00 0,00 0 0 sdc 0,00 0,00 0,00 0 0 sdc 236,33 117522,67 0,00 352568 0 sdc 239,67 117616,00 0,00 352848 0 sdc 233,00 114457,33 0,00 343372 0 sdc 228,00 112152,00 0,00 336456 0 sdc 220,33 108226,67 0,00 324680 0 sdc 215,00 105750,67 0,00 317252 0 sdc 205,00 100630,67 0,00 301892 0 sdc 191,33 94057,33 0,00 282172 0 sdc 187,33 91925,33 0,00 275776 0 sdc 176,67 86888,00 0,00 260664 0 sdc 162,00 79633,33 0,00 238900 0 sdc 148,33 72890,67 0,00 218672 0 sdc 114,00 44477,33 0,00 133432 0 sdc 70,33 281,33 0,00 844 0 sdc 72,67 290,67 0,00 872 0 sdc 70,00 280,00 0,00 840 0 sdc 70,67 282,67 0,00 848 0 sdc 26,00 104,00 0,00 312 0 sdc 0,00 0,00 0,00 0 0 mdadm RAID1 (/dev/sdc5 + /dev/sdd5 - 6Gb partitions) Device: tps kB_read/s kB_wrtn/s kB_read kB_wrtn md99 6,51 776,53 0,00 3899548 0 md99 0,00 0,00 0,00 0 0 md99 0,00 0,00 0,00 0 0 md99 0,00 0,00 0,00 0 0 md99 0,00 0,00 0,00 0 0 md99 325,00 40222,67 0,00 120668 0 md99 993,33 121786,67 0,00 365360 0 md99 993,33 121786,67 0,00 365360 0 md99 993,33 121786,67 0,00 365360 0 md99 943,67 115697,33 0,00 347092 0 md99 993,33 121786,67 0,00 365360 0 md99 993,33 121786,67 0,00 365360 0 md99 993,33 121786,67 0,00 365360 0 md99 993,33 121786,67 0,00 365360 0 md99 943,67 115697,33 0,00 347092 0 md99 993,33 121786,67 0,00 365360 0 md99 184,67 6629,33 0,00 19888 0 md99 138,67 554,67 0,00 1664 0 md99 59,67 238,67 0,00 716 0 mdadm RAID10,f2 (/dev/sdc5 + /dev/sdd5 - 6Gb partitions) Device: tps kB_read/s kB_wrtn/s kB_read kB_wrtn md99 55,04 3872,47 35,97 14288808 132712 md99 0,00 0,00 0,00 0 0 md99 1756,67 149640,00 0,00 448920 0 md99 2578,33 219462,67 0,00 658388 0 md99 2442,33 207912,00 0,00 623736 0 md99 2578,33 219462,67 0,00 658388 0 md99 2578,00 219462,67 0,00 658388 0 md99 2578,33 219462,67 0,00 658388 0 md99 2578,00 219462,67 0,00 658388 0 md99 2578,33 219462,67 0,00 658388 0 md99 2713,67 231013,33 0,00 693040 0 md99 2578,00 219462,67 0,00 658388 0 md99 2557,33 217664,00 0,00 652992 0 md99 152,00 608,00 0,00 1824 0 md99 154,33 617,33 0,00 1852 0 md99 27,00 108,00 0,00 324 0 md99 75,86 5642,46 35,12 21320212 132712 md99 0,00 0,00 0,00 0 0 Is iostat output wrong ? Are these reading speed and volume wrong ? Do I have to rely on this or not ? > You really need to read and comprehend much more about md, or simply > listen to an expert: > > For two disks, use RAID1. PERIOD. End of story. Screwing with > anything else is a massive waste of your time. If you have 3 or more > disks, then you can worry about layouts. Could you also send this advice to Debian people ? Because the layout current in use inside the official Wheezy Debian installer for a 2 disks system is RAID10,f2. It is may be time to open a bug for this. > > -- > Stan > Best regards, -- Jean-Marc <[email protected]> -- To UNSUBSCRIBE, email to [email protected] with a subject of "unsubscribe". Trouble? Contact [email protected] Archive: http://lists.debian.org/[email protected]
