Re: measuring RAID arrays performances
On Sat, 25 May 2013 18:32:59 -0500
Stan Hoeppner <stan@hardwarefreak.com> 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 <jean-marc@6jf.be>
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