* writes raid-6 building
@ 2009-07-28 1:09 Tirumala Reddy Marri
2009-07-28 6:48 ` NeilBrown
0 siblings, 1 reply; 2+ messages in thread
From: Tirumala Reddy Marri @ 2009-07-28 1:09 UTC (permalink / raw)
To: linux-raid
While raid-6 is building I noticed writes are going on to all the
drivers. Whereas in raid-5 I see writes happening to only one drive.
Any clue ?
---------- iostat dump for raid-6 ---
Device: tps MB_read/s MB_wrtn/s MB_read MB_wrtn
sda 152.76 23.81 3.74 47 7
sdb 181.91 25.35 5.50 50 10
sdc 161.31 24.84 3.30 49 6
sdd 153.77 23.52 4.02 46 8
sde 169.85 26.29 3.27 52 6
sdf 0.00 0.00 0.00 0 0
sdg 0.00 0.00 0.00 0 0
sdh 0.00 0.00 0.00 0 0
sdi 0.00 0.00 0.00 0 0
Device: tps MB_read/s MB_wrtn/s MB_read MB_wrtn
sda 152.02 24.05 3.44 47 6
sdb 168.18 26.23 4.14 51 8
sdc 163.64 22.76 3.69 45 7
sdd 166.67 24.37 4.04 48 8
sde 166.16 24.78 3.57 49 7
sdf 0.00 0.00 0.00 0 0
sdg 0.00 0.00 0.00 0 0
sdh 0.00 0.00 0.00 0 0
sdi 0.00 0.00 0.00 0 0
---------------
Thanks,
Marri
^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: writes raid-6 building
2009-07-28 1:09 writes raid-6 building Tirumala Reddy Marri
@ 2009-07-28 6:48 ` NeilBrown
0 siblings, 0 replies; 2+ messages in thread
From: NeilBrown @ 2009-07-28 6:48 UTC (permalink / raw)
To: Tirumala Reddy Marri; +Cc: linux-raid
On Tue, July 28, 2009 11:09 am, Tirumala Reddy Marri wrote:
> While raid-6 is building I noticed writes are going on to all the
> drivers. Whereas in raid-5 I see writes happening to only one drive.
> Any clue ?
Because raid5 != raid6......
For raid5, mdadm creates a degraded array and recovers to a spare.
So it only writes to the spare.
For raid6, mdadm doesn't try to be so clever (the tradeoffs are difference)
and just creates a non-clean array so all the P and Q blocks get
written.
NeilBrown
>
> ---------- iostat dump for raid-6 ---
> Device: tps MB_read/s MB_wrtn/s MB_read MB_wrtn
> sda 152.76 23.81 3.74 47 7
> sdb 181.91 25.35 5.50 50 10
> sdc 161.31 24.84 3.30 49 6
> sdd 153.77 23.52 4.02 46 8
> sde 169.85 26.29 3.27 52 6
> sdf 0.00 0.00 0.00 0 0
> sdg 0.00 0.00 0.00 0 0
> sdh 0.00 0.00 0.00 0 0
> sdi 0.00 0.00 0.00 0 0
>
> Device: tps MB_read/s MB_wrtn/s MB_read MB_wrtn
> sda 152.02 24.05 3.44 47 6
> sdb 168.18 26.23 4.14 51 8
> sdc 163.64 22.76 3.69 45 7
> sdd 166.67 24.37 4.04 48 8
> sde 166.16 24.78 3.57 49 7
> sdf 0.00 0.00 0.00 0 0
> sdg 0.00 0.00 0.00 0 0
> sdh 0.00 0.00 0.00 0 0
> sdi 0.00 0.00 0.00 0 0
> ---------------
> Thanks,
> Marri
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