Expanding RAID array?

Expanding RAID array?

[John Rowe]

I have a 5-disk RAID5 array. Is it possible to add disks to increase the
array size and/or convert it to RAID6? (Indeed, what is the status of
RAID6?)

Thanks

John

Re: Expanding RAID array?

[Neil Brown]

On Monday January 16, rowe@excc.ex.ac.uk wrote:
> I have a 5-disk RAID5 array. Is it possible to add disks to increase the
> array size and/or convert it to RAID6? (Indeed, what is the status of
> RAID6?)

- add disks to increase size of raid5
    Possible offline with raidreconfig
    Possible online with alpha-quality patches that I am
      working on today. Will publish for experimentation/testing
      later this week.  Hopefully stable by late Feb.

- add disks to convert to raid6.
    I don't think this is possible, but you should check the latest
    raid reconfig.
    Might be supported online with a limited raid6 in which the Q
    syndrome (second 'parity' block) isn't rotated among disks.

- status of RAID6
    I believe it is as stable/reliable as raid5.

NeilBrown

Re: Expanding RAID array?

[Gordon Henderson]

On Tue, 17 Jan 2006, Neil Brown wrote:

> - status of RAID6
>     I believe it is as stable/reliable as raid5.

FWIW: I've been using RAID-6 since early last year in production
environments and so-far so good. Kernels 2.6.11 to 2.6.15 (on a Dell 2850
server I'm building tonight with 6 drives). I did have some early issues
with it, but it was actually due to "intersting" hardware... I've not had
a disk failure for real yet, but it's "just worked" every time I've done
tests on it.

Gordon

Re: Expanding RAID array?

[JaniD++]

Hi,

----- Original Message ----- 
From: "Neil Brown" <neilb@suse.de>
To: "John Rowe" <rowe@excc.ex.ac.uk>
Cc: <linux-raid@vger.kernel.org>
Sent: Monday, January 16, 2006 11:37 PM
Subject: Re: Expanding RAID array?


> On Monday January 16, rowe@excc.ex.ac.uk wrote:
> > I have a 5-disk RAID5 array. Is it possible to add disks to increase the
> > array size and/or convert it to RAID6? (Indeed, what is the status of
> > RAID6?)
>
> - add disks to increase size of raid5
>     Possible offline with raidreconfig
>     Possible online with alpha-quality patches that I am
>       working on today. Will publish for experimentation/testing
>       later this week.  Hopefully stable by late Feb.

This patch will can do also chunksize conversion? :-)
And / or converting from N disk to N disk with different chunksize?

I think i will test it if i can get a copy. :-)

Cheers,
Janos

Re: Expanding RAID array?

[Jacob Schmidt Madsen]

Hey,

I was wondering where I can find raidreconfig? google doesnt seem to
know a website for it.

Gordon Henderson wrote:
> On Tue, 17 Jan 2006, Neil Brown wrote:
>
>   
>> - status of RAID6
>>     I believe it is as stable/reliable as raid5.
>>     
>
> FWIW: I've been using RAID-6 since early last year in production
> environments and so-far so good. Kernels 2.6.11 to 2.6.15 (on a Dell 2850
> server I'm building tonight with 6 drives). I did have some early issues
> with it, but it was actually due to "intersting" hardware... I've not had
> a disk failure for real yet, but it's "just worked" every time I've done
> tests on it.
>
> Gordon
> -
> To unsubscribe from this list: send the line "unsubscribe linux-raid" in
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> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>
>   

Re: Expanding RAID array?

[Neil Brown]

On Tuesday January 17, djani22@dynamicweb.hu wrote:
> >
> > - add disks to increase size of raid5
> >     Possible offline with raidreconfig
> >     Possible online with alpha-quality patches that I am
> >       working on today. Will publish for experimentation/testing
> >       later this week.  Hopefully stable by late Feb.
> 
> This patch will can do also chunksize conversion? :-)

Not currently, but it shouldn't be too hard to add.

> And / or converting from N disk to N disk with different chunksize?

No.  This is impossible to do both efficiently and safely with NVRAM.
Even if you give up "efficiently" you need some temporary storage space.

You would need to 
  copy a stripe to some temporary storage
  Update the metadata to record that the stripe has moved
  copy the stripe back with the new geometry 
  Update the metadata to record the movement
 repeat

It certainly could be done, but I doubt the demand would be high
enough to justify it.

The situation is similar for raid5-raid6 or raid0-raid5 conversions
that done increase the size of the array (i.e. only add one device).
They require update-in-place which is hard to do in a way that still
protects your data if there is a power failure.

NeilBrown

Re: Expanding RAID array?

[Brad Campbell]

Neil Brown wrote:

> - add disks to convert to raid6.
>     I don't think this is possible, but you should check the latest
>     raid reconfig.

It's not. I started work on it Feb last year but then real life got in the way again.
In the longer term, I think raidreconf as it stands is going to die (mainly because it's 
infrastructure relies on the old raidtab architecture). I thought about perhaps porting it as an 
addon to mdadm, but then I ran out of drives/machines/time to test it on.

>     Might be supported online with a limited raid6 in which the Q
>     syndrome (second 'parity' block) isn't rotated among disks.

In theory I would have thought it not that much different than a raid-5 expand, just inserting an 
extra block for the Q syndrome.

> - status of RAID6
>     I believe it is as stable/reliable as raid5.

Mine has been running since Feb last year with fairly moderate use and no hiccups.
I have just upgraded to the latest 2.6.15-git on that machine to give some of the newer raid patches 
(like check & repair) a whirl. Seems fairly solid.

Let's say I've never had any raid-6 related data loss, or even near misses, but it has saved my 
bacon in 2 dual drive failures in the last year.

Oh, and the new read and check code (rather than just rebuild the parity blocks) shaves about 1 hour 
of what was an 11 hour rebuild time on this particular raid-6. Thanks Neil!

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: Expanding RAID array?

[Eyal Lebedinsky]

Jacob Schmidt Madsen wrote:
> Hey,
> 
> I was wondering where I can find raidreconfig? google doesnt seem to
> know a website for it.

http://unthought.net/raidreconf/index.shtml

-- 
Eyal Lebedinsky (eyal@eyal.emu.id.au) <http://samba.org/eyal/>
	attach .zip as .dat

Re: Expanding RAID array?

[Turbo Fredriksson]

Quoting Gordon Henderson <gordon@drogon.net>:

> On Tue, 17 Jan 2006, Neil Brown wrote:
>
>> - status of RAID6
>>     I believe it is as stable/reliable as raid5.
>
> FWIW: I've been using RAID-6 since early last year in production
> environments and so-far so good.

Ditto. On a VERY loaded system (so loaded that it crash every now and
then because of the load). Haven't had ANY trouble what so ever with
RAID6. I'm very (!) happy with it!

This on 4x9Gb + 2 spares. Use it on the system/root filesystem only
though... Which isn't THAT loaded now when I think about it...

If I could, i'd convert all my RAID5 sets to RAID6. But I don't have
time for the downtime. I'll monitor this subject closely though... :)

> Kernels 2.6.11 to 2.6.15 (on a Dell 2850 server I'm building tonight with 6 drives).

Mine is a 2.6.12.4 on a Sun Blade 1000 (2x750MHz UltraSPARC III) CPU's
(now) with 2Gb mem...

> I've not had a disk failure for real yet, but it's "just worked" every time I've done
> tests on it.

Same here. I've been fortunate to not have a disk crash so I can't
say how stable/good RAID6 is if disks start krashing :)
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