* Changing Chunk Size on Array
@ 2010-07-17 21:15 Leslie Rhorer
2010-07-17 21:30 ` Roman Mamedov
2010-07-19 23:49 ` Neil Brown
0 siblings, 2 replies; 6+ messages in thread
From: Leslie Rhorer @ 2010-07-17 21:15 UTC (permalink / raw)
To: linux-raid
I'm thinking about changing the chunk size on one of my arrays in
order to potentially improve performance. The man page rather suggests -c
is a vlaid option under Grow mode, although it doesn't specifically say
mdadm supports it under --grow. Is it indeed supported under mdadm 2.6.7.2
and kernel 2.6.26-2? Assuming so, I would like to know a bit more about the
change before issuing the command. Speficialy, what are the details of the
process? Does the entire (RAID 6) array have to be re-written, such as is
the case with adding a drive to the array? Does the recovery start
immediately? Can it be interrupted and then continue at a later time?
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: Changing Chunk Size on Array
2010-07-17 21:15 Changing Chunk Size on Array Leslie Rhorer
@ 2010-07-17 21:30 ` Roman Mamedov
2010-07-17 21:45 ` Leslie Rhorer
2010-07-19 23:49 ` Neil Brown
1 sibling, 1 reply; 6+ messages in thread
From: Roman Mamedov @ 2010-07-17 21:30 UTC (permalink / raw)
To: Leslie Rhorer; +Cc: linux-raid
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On Sat, 17 Jul 2010 16:15:55 -0500
"Leslie Rhorer" <lrhorer@satx.rr.com> wrote:
>
> I'm thinking about changing the chunk size on one of my arrays in
> order to potentially improve performance. The man page rather suggests -c
> is a vlaid option under Grow mode, although it doesn't specifically say
> mdadm supports it under --grow. Is it indeed supported under mdadm 2.6.7.2
> and kernel 2.6.26-2? Assuming so, I would like to know a bit more about the
> change before issuing the command. Speficialy, what are the details of the
> process? Does the entire (RAID 6) array have to be re-written, such as is
> the case with adding a drive to the array? Does the recovery start
> immediately? Can it be interrupted and then continue at a later time?
Out of curiosity, which chunk size do you have, and which you want to change
it to, and do you expect the new size to be faster based on any tests?
--
With respect,
Roman
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^ permalink raw reply [flat|nested] 6+ messages in thread
* RE: Changing Chunk Size on Array
2010-07-17 21:30 ` Roman Mamedov
@ 2010-07-17 21:45 ` Leslie Rhorer
0 siblings, 0 replies; 6+ messages in thread
From: Leslie Rhorer @ 2010-07-17 21:45 UTC (permalink / raw)
To: 'Roman Mamedov'; +Cc: linux-raid
> -----Original Message-----
> From: Roman Mamedov [mailto:roman@rm.pp.ru]
> Sent: Saturday, July 17, 2010 4:31 PM
> To: Leslie Rhorer
> Cc: linux-raid@vger.kernel.org
> Subject: Re: Changing Chunk Size on Array
>
> On Sat, 17 Jul 2010 16:15:55 -0500
> "Leslie Rhorer" <lrhorer@satx.rr.com> wrote:
>
> >
> > I'm thinking about changing the chunk size on one of my arrays in
> > order to potentially improve performance. The man page rather suggests
> -c
> > is a vlaid option under Grow mode, although it doesn't specifically say
> > mdadm supports it under --grow. Is it indeed supported under mdadm
> 2.6.7.2
> > and kernel 2.6.26-2? Assuming so, I would like to know a bit more about
> the
> > change before issuing the command. Speficialy, what are the details of
> the
> > process? Does the entire (RAID 6) array have to be re-written, such as
> is
> > the case with adding a drive to the array? Does the recovery start
> > immediately? Can it be interrupted and then continue at a later time?
>
> Out of curiosity, which chunk size do you have, and which you want to
> change
> it to, and do you expect the new size to be faster based on any tests?
The current chunk is 256K. One of my other arrays on a nearly
identical platform seems to have better performance at 1024K. I haven't
made any decisions, yet on what the new value would be, or even in fact if I
will actually consider doing it. I'm still at the evaluation stage. Most
of the files on the array are in the 10G - 30G range in size, and they are
generally read and written sequentially. The individual members are
thirteen 1T drives in an 11T RAID6 array.
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: Changing Chunk Size on Array
2010-07-17 21:15 Changing Chunk Size on Array Leslie Rhorer
2010-07-17 21:30 ` Roman Mamedov
@ 2010-07-19 23:49 ` Neil Brown
2010-07-20 0:17 ` Konstantin Svist
2010-07-21 5:52 ` Leslie Rhorer
1 sibling, 2 replies; 6+ messages in thread
From: Neil Brown @ 2010-07-19 23:49 UTC (permalink / raw)
To: Leslie Rhorer; +Cc: linux-raid
On Sat, 17 Jul 2010 16:15:55 -0500
"Leslie Rhorer" <lrhorer@satx.rr.com> wrote:
>
> I'm thinking about changing the chunk size on one of my arrays in
> order to potentially improve performance. The man page rather suggests -c
> is a vlaid option under Grow mode, although it doesn't specifically say
> mdadm supports it under --grow. Is it indeed supported under mdadm 2.6.7.2
> and kernel 2.6.26-2? Assuming so, I would like to know a bit more about the
> change before issuing the command. Speficialy, what are the details of the
> process? Does the entire (RAID 6) array have to be re-written, such as is
> the case with adding a drive to the array? Does the recovery start
> immediately? Can it be interrupted and then continue at a later time?
Yes, you can change chunksize with --grow.
I think you need mdadm-3.1.2 and kernel 2.6.32 though (version numbers might
not be accurate, but are close).
Yes, the entire array gets re-written just like adding an extra device.
The reshape does start immediately.
If you shutdown or crash, then on restart the reshape will pick up where it
left off.
NeilBrown
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: Changing Chunk Size on Array
2010-07-19 23:49 ` Neil Brown
@ 2010-07-20 0:17 ` Konstantin Svist
2010-07-21 5:52 ` Leslie Rhorer
1 sibling, 0 replies; 6+ messages in thread
From: Konstantin Svist @ 2010-07-20 0:17 UTC (permalink / raw)
To: linux-raid
On 07/19/2010 04:49 PM, Neil Brown wrote:
> On Sat, 17 Jul 2010 16:15:55 -0500
> "Leslie Rhorer"<lrhorer@satx.rr.com> wrote:
>
>> I'm thinking about changing the chunk size on one of my arrays in
>> order to potentially improve performance. The man page rather suggests -c
>> is a vlaid option under Grow mode, although it doesn't specifically say
>> mdadm supports it under --grow. Is it indeed supported under mdadm 2.6.7.2
>> and kernel 2.6.26-2? Assuming so, I would like to know a bit more about the
>> change before issuing the command. Speficialy, what are the details of the
>> process? Does the entire (RAID 6) array have to be re-written, such as is
>> the case with adding a drive to the array? Does the recovery start
>> immediately? Can it be interrupted and then continue at a later time?
> Yes, you can change chunksize with --grow.
> I think you need mdadm-3.1.2 and kernel 2.6.32 though (version numbers might
> not be accurate, but are close).
>
> Yes, the entire array gets re-written just like adding an extra device.
> The reshape does start immediately.
> If you shutdown or crash, then on restart the reshape will pick up where it
> left off.
I ran mine with mdadm v3.1.2 on 2.6.33.6-147.fc13.x86_64 (Fedora)
Too bad I screwed up the FS by shrinking the array too much beforehand -
now I have no idea whether it would've worked or not.
^ permalink raw reply [flat|nested] 6+ messages in thread
* RE: Changing Chunk Size on Array
2010-07-19 23:49 ` Neil Brown
2010-07-20 0:17 ` Konstantin Svist
@ 2010-07-21 5:52 ` Leslie Rhorer
1 sibling, 0 replies; 6+ messages in thread
From: Leslie Rhorer @ 2010-07-21 5:52 UTC (permalink / raw)
To: 'Neil Brown'; +Cc: linux-raid
> > I'm thinking about changing the chunk size on one of my arrays in
> > order to potentially improve performance. The man page rather suggests
> -c
> > is a vlaid option under Grow mode, although it doesn't specifically say
> > mdadm supports it under --grow. Is it indeed supported under mdadm
> 2.6.7.2
> > and kernel 2.6.26-2? Assuming so, I would like to know a bit more about
> the
> > change before issuing the command. Speficialy, what are the details of
> the
> > process? Does the entire (RAID 6) array have to be re-written, such as
> is
> > the case with adding a drive to the array? Does the recovery start
> > immediately? Can it be interrupted and then continue at a later time?
>
> Yes, you can change chunksize with --grow.
> I think you need mdadm-3.1.2 and kernel 2.6.32 though (version numbers
> might
> not be accurate, but are close).
Oh, well. I'll have to upgrade that system one of these days, but
definitely not right now. 'Possibly soon after "Squeeze" goes gold, but
definitely not before.
> Yes, the entire array gets re-written just like adding an extra device.
> The reshape does start immediately.
> If you shutdown or crash, then on restart the reshape will pick up where
> it
Thanks.
^ permalink raw reply [flat|nested] 6+ messages in thread
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2010-07-17 21:15 Changing Chunk Size on Array Leslie Rhorer
2010-07-17 21:30 ` Roman Mamedov
2010-07-17 21:45 ` Leslie Rhorer
2010-07-19 23:49 ` Neil Brown
2010-07-20 0:17 ` Konstantin Svist
2010-07-21 5:52 ` Leslie Rhorer
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