skip raid5 reconstruction

skip raid5 reconstruction

[Ming Zhang]

Hi folks

I am testing some HW performance with raid5 with 2.4.x kenrel.

It is really troublesome every time I create a raid5, wait 4 hours for
reconstruction, and then test some data and then recreate another one
and wait again. I wonder if there is any hack or option available to
create a raid5 without reconstruct the parity disk. I just have interest
to test the performance so do not care about data correctness at this
stage.

Thanks!


Ming

Re: skip raid5 reconstruction

[Brad Campbell]

Ming Zhang wrote:
> Hi folks
> 
> I am testing some HW performance with raid5 with 2.4.x kenrel.
> 
> It is really troublesome every time I create a raid5, wait 4 hours for
> reconstruction, and then test some data and then recreate another one
> and wait again. I wonder if there is any hack or option available to
> create a raid5 without reconstruct the parity disk. I just have interest
> to test the performance so do not care about data correctness at this
> stage.

I did a similar thing a while back.
I created the raid and waited for it to sync, I then make dd copies of the raid superblocks.
When I blew it up I just dd the clean superblocks back again (saved a 12 hour rebuild time)

Having just thought about what you wrote, I guess you are building the raid in different
configurationes each time, so my method might not be good for you.

Regards,
Brad
-- 
"Human beings, who are almost unique in having the ability
to learn from the experience of others, are also remarkable
for their apparent disinclination to do so." -- Douglas Adams

Re: skip raid5 reconstruction

[Ming Zhang]

On Wed, 2005-07-06 at 10:47 +0400, Brad Campbell wrote:
> Ming Zhang wrote:
> > Hi folks
> > 
> > I am testing some HW performance with raid5 with 2.4.x kenrel.
> > 
> > It is really troublesome every time I create a raid5, wait 4 hours for
> > reconstruction, and then test some data and then recreate another one
> > and wait again. I wonder if there is any hack or option available to
> > create a raid5 without reconstruct the parity disk. I just have interest
> > to test the performance so do not care about data correctness at this
> > stage.
> 
> I did a similar thing a while back.
> I created the raid and waited for it to sync, I then make dd copies of the raid superblocks.
> When I blew it up I just dd the clean superblocks back again (saved a 12 hour rebuild time)
interesting to know about this. u just check the dmesg and see where is
the sb and then u dd it out and dd back later?


> 
> Having just thought about what you wrote, I guess you are building the raid in different
> configurationes each time, so my method might not be good for you.
> 
yes, i changed it many times.


thx anyway!


Ming



> Regards,
> Brad

Re: skip raid5 reconstruction

[Brad Campbell]

Ming Zhang wrote:

>>I did a similar thing a while back.
>>I created the raid and waited for it to sync, I then make dd copies of the raid superblocks.
>>When I blew it up I just dd the clean superblocks back again (saved a 12 hour rebuild time)
> 
> interesting to know about this. u just check the dmesg and see where is
> the sb and then u dd it out and dd back later?

Actually, I used blockdev to get the device size and then just copied the last 64kb from memory.. 
It's a bit hazy now but that's pretty close I think

Regards
Brad
-- 
"Human beings, who are almost unique in having the ability
to learn from the experience of others, are also remarkable
for their apparent disinclination to do so." -- Douglas Adams

Re: skip raid5 reconstruction

[Ming Zhang]

On Fri, 2005-07-08 at 22:14 +0400, Brad Campbell wrote:
> Ming Zhang wrote:
> 
> >>I did a similar thing a while back.
> >>I created the raid and waited for it to sync, I then make dd copies of the raid superblocks.
> >>When I blew it up I just dd the clean superblocks back again (saved a 12 hour rebuild time)
> > 
> > interesting to know about this. u just check the dmesg and see where is
> > the sb and then u dd it out and dd back later?
> 
> Actually, I used blockdev to get the device size and then just copied the last 64kb from memory.. 
> It's a bit hazy now but that's pretty close I think
> 
:P that is a good method!

thx

ming

> Regards
> Brad

Re: skip raid5 reconstruction

[Michael Tokarev]

Ming Zhang wrote:
> Hi folks
> 
> I am testing some HW performance with raid5 with 2.4.x kenrel.
> 
> It is really troublesome every time I create a raid5, wait 4 hours for
> reconstruction, and then test some data and then recreate another one
> and wait again. I wonder if there is any hack or option available to
> create a raid5 without reconstruct the parity disk. I just have interest
> to test the performance so do not care about data correctness at this
> stage.

Maybe try smaller partitions?

/mjt

Re: skip raid5 reconstruction

[Ming Zhang]

Thanks, that is a workaround as well. :P

I already solve this by using mkraid.

Ming


On Wed, 2005-07-06 at 19:45 +0400, Michael Tokarev wrote:
> Ming Zhang wrote:
> > Hi folks
> > 
> > I am testing some HW performance with raid5 with 2.4.x kenrel.
> > 
> > It is really troublesome every time I create a raid5, wait 4 hours for
> > reconstruction, and then test some data and then recreate another one
> > and wait again. I wonder if there is any hack or option available to
> > create a raid5 without reconstruct the parity disk. I just have interest
> > to test the performance so do not care about data correctness at this
> > stage.
> 
> Maybe try smaller partitions?
> 
> /mjt