From: NeilBrown <neilb@suse.de>
To: "Karsten Römke" <k.roemke@gmx.de>
Cc: linux-raid@vger.kernel.org
Subject: Re: misunderstanding of spare and raid devices? - and one question more
Date: Fri, 1 Jul 2011 07:28:55 +1000 [thread overview]
Message-ID: <20110701072855.69ee763b@notabene.brown> (raw)
In-Reply-To: <4E0C8685.3020806@gmx.de>
On Thu, 30 Jun 2011 16:21:57 +0200 Karsten Römke <k.roemke@gmx.de> 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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next prev parent reply other threads:[~2011-06-30 21:28 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-06-30 10:51 misunderstanding of spare and raid devices? Karsten Römke
2011-06-30 10:58 ` Robin Hill
2011-06-30 13:09 ` Karsten Römke
2011-06-30 11:30 ` John Robinson
2011-06-30 12:32 ` Phil Turmel
2011-06-30 12:52 ` misunderstanding of spare and raid devices? - and one question more Karsten Römke
2011-06-30 13:34 ` Phil Turmel
2011-06-30 14:05 ` Karsten Römke
2011-06-30 14:21 ` Karsten Römke
2011-06-30 14:44 ` Phil Turmel
2011-07-02 8:34 ` Karsten Römke
2011-07-02 9:42 ` David Brown
2011-06-30 21:28 ` NeilBrown [this message]
2011-07-01 7:23 ` David Brown
2011-07-01 8:50 ` Robin Hill
2011-07-01 10:18 ` David Brown
2011-07-01 11:29 ` Robin Hill
2011-07-01 12:45 ` David Brown
2011-07-01 13:02 ` NeilBrown
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