On Thu, 30 Jun 2011 16:21:57 +0200 Karsten Römke <k.roemke@xxxxxx> wrote:
> Hi Phil
> >
> > If your CPU has free cycles, I suggest you run raid6 instead of raid5+spare.
> >
> > Phil
> >
> I started the raid 6 array and get:
>
> Personalities : [raid0] [raid1] [raid10] [raid6] [raid5] [raid4]
> md0 : active raid6 sde5[4] sdd5[3] sdc5[2] sdb2[1] sda3[0]
> 13759296 blocks level 6, 64k chunk, algorithm 2 [5/5] [UUUUU]
> [=================>...] resync = 87.4% (4013184/4586432) finish=0.4min speed=20180K/sec
^^^^^^
Note: resync
>
> when I started the raid 5 array I get
>
> md0 : active raid5 sdd5[4] sde5[5](S) sdc5[2] sdb2[1] sda3[0]
> 13759296 blocks level 5, 64k chunk, algorithm 2 [4/3] [UUU_]
> [=>...................] recovery = 6.2% (286656/4586432) finish=0.9min speed=71664K/sec
^^^^^^^^
Note: recovery.
>
> so I have to expect a three times less write speed - or is this calculation
> to simple ?
>
You are comparing two different things, neither of which is write speed.
If you want to measure write speed, you should try writing and measure that.
When you create a RAID5 mdadm deliberately triggers recovery rather than
resync as it is likely to be faster. This is why you see a missed device and
an extra spare. I don't remember why it doesn't with RAID6.
NeilBrown
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