From: NeilBrown <neilb@suse.de>
To: Piergiorgio Sartor <piergiorgio.sartor@nexgo.de>
Cc: linux-raid@vger.kernel.org
Subject: Re: User space RAID-6 access
Date: Sun, 6 Feb 2011 07:58:20 +1100 [thread overview]
Message-ID: <20110206075820.08fc19c9@notabene.brown> (raw)
In-Reply-To: <20110205173334.GA5952@lazy.lzy>
On Sat, 5 Feb 2011 18:33:34 +0100 Piergiorgio Sartor
<piergiorgio.sartor@nexgo.de> wrote:
> > Look in the mdadm source code, particularly at restripe.c
> >
> > Also
> > make test_stripe
> >
> > make a program the the test suite uses for verify data correctness.
> >
> > That should give you enough hints to get you started.
>
> Hi Neil,
>
> I'm trying to use the "test_stripe" binary, just to
> confirm the operation, in test mode (no save nor restore).
>
> Unfortunately, it seems not work properly, in my hands.
>
> I created a 4 disks RAID-6 (/dev/loop[0-3]), with:
>
> mdadm -C /dev/md111 -l 6 -n 4 --chunk=64 /dev/loop[0-3]
>
> Filled the array from urandom:
>
> dd if=/dev/urandom of=/dev/md111
>
> And tried:
>
> ./test_stripe test file_test.raw 4 65536 6 2 65536 $[ 65536 * 3 ] /dev/loop[0-3]
>
> This returns:
>
> 0->0
> 1->1
> P(2) wrong at 1
> Q(3) wrong at 1
> 0->3
> 1->0
> P(1) wrong at 2
> Q(2) wrong at 2
> 0->2
> 1->3
> P(0) wrong at 3
> Q(1) wrong at 3
>
> The array filled with "0" does not return any error.
>
> Am'I missing something or the code has problems?
>
> An other question, I noticed the code uses an array of
> "offsets" which seem to be filled with "0" and never
> changed.
> Is this really wanted?
> Is the offset information the one found per component
> using "mdadm -E ..." or /sys/class/block/mdX/md/rdX/offset?
> What's the relation with the "start" parameter of "test_stripe"?
>
> Thanks in advance for any hints or suggestions.
test_stripe assumes that the data starts at the start of each device.
AS you are using 1.2 metadata (the default), data starts about 1M in to
the device (I think - you can check with --examine)
You could fix test_stripe to put the right value in the 'offsets' array,
or you could create the array with 1.0 or 0.90 metadata.
NeilBrown
>
> The md device is:
>
> /dev/md111:
> Version : 1.2
> Creation Time : Sat Feb 5 17:48:49 2011
> Raid Level : raid6
> Array Size : 524160 (511.96 MiB 536.74 MB)
> Used Dev Size : 262080 (255.98 MiB 268.37 MB)
> Raid Devices : 4
> Total Devices : 4
> Persistence : Superblock is persistent
>
> Update Time : Sat Feb 5 18:19:45 2011
> State : clean
> Active Devices : 4
> Working Devices : 4
> Failed Devices : 0
> Spare Devices : 0
>
> Layout : left-symmetric
> Chunk Size : 64K
>
> Name : lazy.lzy:111 (local to host lazy.lzy)
> UUID : b794fb80:c4006853:47761570:3d97a1d2
> Events : 42
>
> Number Major Minor RaidDevice State
> 0 7 0 0 active sync /dev/loop0
> 1 7 1 1 active sync /dev/loop1
> 2 7 2 2 active sync /dev/loop2
> 3 7 3 3 active sync /dev/loop3
>
> bye,
>
next prev parent reply other threads:[~2011-02-05 20:58 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-01-31 20:20 User space RAID-6 access Piergiorgio Sartor
2011-01-31 20:52 ` NeilBrown
2011-02-01 19:21 ` Piergiorgio Sartor
2011-02-01 20:14 ` John Robinson
2011-02-01 20:18 ` NeilBrown
2011-02-01 21:00 ` Piergiorgio Sartor
2011-02-05 17:33 ` Piergiorgio Sartor
2011-02-05 20:58 ` NeilBrown [this message]
2011-02-07 22:24 ` [PATCH] " Piergiorgio Sartor
2011-02-07 22:49 ` NeilBrown
2011-02-09 18:47 ` Piergiorgio Sartor
2011-02-17 6:23 ` NeilBrown
2011-02-17 20:01 ` Piergiorgio Sartor
2011-02-18 23:02 ` Piergiorgio Sartor
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