Raid0 and drive failure.

Raid0 and drive failure.

[Henti Smith]

Good day.

This is likely a newbie question, but I just need to confirm. If you
have 3 x 100GB drives in RAID0 and one drive dies this will result in
total data loss correct?

Is there no way to loose only the data that resides (even partly) on
the missing drive but retain the rest of the data ?

Regards
Henti

Re: Raid0 and drive failure.

[Henti Smith]

On Fri, Sep 16, 2011 at 4:49 PM, Leonidas Spyropoulos
<artafinde@gmail.com> wrote:
> On Sep 16, 2011 1:25 PM, "Henti Smith" <henti@geekware.co.za> wrote:
>> Good day.
>>
> Hello

Hi

>> This is likely a newbie question, but I just need to confirm. If you
>> have 3 x 100GB drives in RAID0 and one drive dies this will result in
>> total data loss correct?
>>
> Yes the data are lost. Read more on how raid 0 works.

I have read on how raid 0 works, I was merely asking about the
implementation of raid0 on btrfs.

>> Is there no way to loose only the data that resides (even partly) on
>> the missing drive but retain the rest of the data ?

This is the more pertinent question, which it seem btrfs can't do currently.

Henti

Re: Raid0 and drive failure.

[Hugo Mills]

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On Fri, Sep 16, 2011 at 05:06:03PM +0200, Henti Smith wrote:
> On Fri, Sep 16, 2011 at 4:49 PM, Leonidas Spyropoulos
> <artafinde@gmail.com> wrote:
> > On Sep 16, 2011 1:25 PM, "Henti Smith" <henti@geekware.co.za> wrote:
> >> This is likely a newbie question, but I just need to confirm. If you
> >> have 3 x 100GB drives in RAID0 and one drive dies this will result in
> >> total data loss correct?
> >>
> > Yes the data are lost. Read more on how raid 0 works.
> 
> I have read on how raid 0 works, I was merely asking about the
> implementation of raid0 on btrfs.
> 
> >> Is there no way to loose only the data that resides (even partly) on
> >> the missing drive but retain the rest of the data ?
> 
> This is the more pertinent question, which it seem btrfs can't do currently.

   btrfs stripes its RAID-0 data across all available disks, so you'd
lose approximately 1/3 of the data for each file. In some cases, you
might get lucky and have a small file that resides entirely on the two
undamaged disks. In that case, it *might* be possible to recover your
data, but I think in general the amount of effort involved to get that
degree of recovery is probably far outweighted by the use of your
backups to restore all of the missing data...

   Hugo.

-- 
=== Hugo Mills: hugo@... carfax.org.uk | darksatanic.net | lug.org.uk ===
  PGP key: 515C238D from wwwkeys.eu.pgp.net or http://www.carfax.org.uk
       --- "Are you the man who rules the Universe?" "Well,  I ---       
                              try not to."                               

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Re: Raid0 and drive failure.

[Henti Smith]

>> This is the more pertinent question, which it seem btrfs can't do cu=
rrently.
>
> =A0 btrfs stripes its RAID-0 data across all available disks, so you'=
d
> lose approximately 1/3 of the data for each file. In some cases, you
> might get lucky and have a small file that resides entirely on the tw=
o
> undamaged disks. In that case, it *might* be possible to recover your
> data, but I think in general the amount of effort involved to get tha=
t
> degree of recovery is probably far outweighted by the use of your
> backups to restore all of the missing data...

That how I understood raid0 as well, so I do understand that, thank you=
=2E

Henti
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Re: Raid0 and drive failure.

[Henti Smith]

On Fri, Sep 16, 2011 at 5:10 PM, Hugo Mills <hugo@carfax.org.uk> wrote:
> On Fri, Sep 16, 2011 at 05:06:03PM +0200, Henti Smith wrote:
>> On Fri, Sep 16, 2011 at 4:49 PM, Leonidas Spyropoulos
>> <artafinde@gmail.com> wrote:
>> > On Sep 16, 2011 1:25 PM, "Henti Smith" <henti@geekware.co.za> wrot=
e:
>> >> This is likely a newbie question, but I just need to confirm. If =
you
>> >> have 3 x 100GB drives in RAID0 and one drive dies this will resul=
t in
>> >> total data loss correct?
>> >>
>> > Yes the data are lost. Read more on how raid 0 works.
>>
>> I have read on how raid 0 works, I was merely asking about the
>> implementation of raid0 on btrfs.
>>
>> >> Is there no way to loose only the data that resides (even partly)=
 on
>> >> the missing drive but retain the rest of the data ?
>>
>> This is the more pertinent question, which it seem btrfs can't do cu=
rrently.
>
> =A0 btrfs stripes its RAID-0 data across all available disks, so you'=
d
> lose approximately 1/3 of the data for each file. In some cases, you
> might get lucky and have a small file that resides entirely on the tw=
o
> undamaged disks. In that case, it *might* be possible to recover your
> data, but I think in general the amount of effort involved to get tha=
t
> degree of recovery is probably far outweighted by the use of your
> backups to restore all of the missing data...
>
> =A0 Hugo.

Hi Hugo, Leonidas, everybody

Sorry to keep this going.

I've read some more on btrfs and one of the features listed as planned
is "Object-level RAID"
What will be the functional advantages of this as opposed to
filesystem level RAID.

Would this not be the place to possibly add features to allow recovery
of raid0 on an object level when a disk in the pool is lost, rather
than loosing all data ?

Henti
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Re: Raid0 and drive failure.

[Hugo Mills]

[-- Attachment #1: Type: text/plain, Size: 3202 bytes --]

On Sat, Sep 17, 2011 at 09:20:28AM +0200, Henti Smith wrote:
> On Fri, Sep 16, 2011 at 5:10 PM, Hugo Mills <hugo@carfax.org.uk> wrote:
> > On Fri, Sep 16, 2011 at 05:06:03PM +0200, Henti Smith wrote:
> >> On Fri, Sep 16, 2011 at 4:49 PM, Leonidas Spyropoulos
> >> <artafinde@gmail.com> wrote:
> >> > On Sep 16, 2011 1:25 PM, "Henti Smith" <henti@geekware.co.za> wrote:
> >> >> This is likely a newbie question, but I just need to confirm. If you
> >> >> have 3 x 100GB drives in RAID0 and one drive dies this will result in
> >> >> total data loss correct?
> >> >>
> >> > Yes the data are lost. Read more on how raid 0 works.
> >>
> >> I have read on how raid 0 works, I was merely asking about the
> >> implementation of raid0 on btrfs.
> >>
> >> >> Is there no way to loose only the data that resides (even partly) on
> >> >> the missing drive but retain the rest of the data ?
> >>
> >> This is the more pertinent question, which it seem btrfs can't do currently.
> >
> >   btrfs stripes its RAID-0 data across all available disks, so you'd
> > lose approximately 1/3 of the data for each file. In some cases, you
> > might get lucky and have a small file that resides entirely on the two
> > undamaged disks. In that case, it *might* be possible to recover your
> > data, but I think in general the amount of effort involved to get that
> > degree of recovery is probably far outweighted by the use of your
> > backups to restore all of the missing data...
> >
> >   Hugo.
> 
> Hi Hugo, Leonidas, everybody
> 
> Sorry to keep this going.
> 
> I've read some more on btrfs and one of the features listed as planned
> is "Object-level RAID"
> What will be the functional advantages of this as opposed to
> filesystem level RAID.

   It'll mean that you can specify that individual files should be
stored with different replication. (e.g. you could give the files
containing your latest novel RAID-6 replication, but your CD
collection RAID-0, all on the same filesystem).

   It'll use exactly the same mechanisms that already exist in btrfs
for replication, but will be configurable at finer levels of
granularity (at least subvolumes, possibly down to individual files).

> Would this not be the place to possibly add features to allow recovery
> of raid0 on an object level when a disk in the pool is lost, rather
> than loosing all data ?

   I'm confused. How would you expect to recover a file on a broken
RAID-0 when half (or 1/3, or whatever) of the data in it has gone away
for good? The file is lost and gone forever. If you care somewhat
about your data, use RAID-1, or -10 (or -5 or -6 when they arrive in
btrfs[1]). If you really care about your data, keep off-machine and
off-site backups -- RAID is not a backup.

   Hugo.

[1] Although I see the demon that picks my .sig quotes has found an
appropriate one again...

-- 
=== Hugo Mills: hugo@... carfax.org.uk | darksatanic.net | lug.org.uk ===
  PGP key: 515C238D from wwwkeys.eu.pgp.net or http://www.carfax.org.uk
         --- Great oxymorons of the world, no. 8: The Latest ---         
                          In Proven Technology                           

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Re: Raid0 and drive failure.

[Henti Smith]

>> I've read some more on btrfs and one of the features listed as plann=
ed
>> is "Object-level RAID"
>> What will be the functional advantages of this as opposed to
>> filesystem level RAID.
>
> =A0 It'll mean that you can specify that individual files should be
> stored with different replication. (e.g. you could give the files
> containing your latest novel RAID-6 replication, but your CD
> collection RAID-0, all on the same filesystem).

Ahh ok this can be very handy, thanks :)

> =A0 It'll use exactly the same mechanisms that already exist in btrfs
> for replication, but will be configurable at finer levels of
> granularity (at least subvolumes, possibly down to individual files).
>
>> Would this not be the place to possibly add features to allow recove=
ry
>> of raid0 on an object level when a disk in the pool is lost, rather
>> than loosing all data ?
>
> =A0 I'm confused. How would you expect to recover a file on a broken
> RAID-0 when half (or 1/3, or whatever) of the data in it has gone awa=
y
> for good? The file is lost and gone forever. If you care somewhat
> about your data, use RAID-1, or -10 (or -5 or -6 when they arrive in
> btrfs[1]). If you really care about your data, keep off-machine and
> off-site backups -- RAID is not a backup.

That's just it, I don't care about my data that is lost when a drive
fails, I care about loosing all the data when only one drive fails.
Hence I'm trying to find out if there is a way to have fault tolerant
drive pooling.
After some more reading linear mode seems to offer the best options if
you can only discard the files in the FS that islost when a drive is
lost, but I'm still looking more into this.

At it's core I'm looking for a way to do something similar windows
drive extender that allows you to pool your drives without loosing all
your data when one drive is lost.

Regards
Henti
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Re: Raid0 and drive failure.

[Hugo Mills]

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On Sat, Sep 17, 2011 at 04:10:44PM +0200, Henti Smith wrote:
> Hugo Mills wrote at some point:
> >   I'm confused. How would you expect to recover a file on a broken
> > RAID-0 when half (or 1/3, or whatever) of the data in it has gone away
> > for good? The file is lost and gone forever. If you care somewhat
> > about your data, use RAID-1, or -10 (or -5 or -6 when they arrive in
> > btrfs[1]). If you really care about your data, keep off-machine and
> > off-site backups -- RAID is not a backup.
> 
> That's just it, I don't care about my data that is lost when a drive
> fails, I care about loosing all the data when only one drive fails.
> Hence I'm trying to find out if there is a way to have fault tolerant
> drive pooling.
> After some more reading linear mode seems to offer the best options if
> you can only discard the files in the FS that islost when a drive is
> lost, but I'm still looking more into this.
> 
> At it's core I'm looking for a way to do something similar windows
> drive extender that allows you to pool your drives without loosing all
> your data when one drive is lost.

   Aaaah, OK. Things become clearer.

   mkfs.btrfs -d single -m raid1 is probably what you want, then.

   Hugo.

-- 
=== Hugo Mills: hugo@... carfax.org.uk | darksatanic.net | lug.org.uk ===
  PGP key: 515C238D from wwwkeys.eu.pgp.net or http://www.carfax.org.uk
         --- Quantum Mechanics: the dreams stuff is made of. ---         

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Re: Raid0 and drive failure.

[Roman Mamedov]

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On Sat, 17 Sep 2011 16:10:44 +0200
Henti Smith <henti@geekware.co.za> wrote:

> At it's core I'm looking for a way to do something similar windows
> drive extender that allows you to pool your drives without loosing all
> your data when one drive is lost.

Use mhddfs: http://romanrm.ru/en/mhddfs
Only one drive's files are lost when that drive fails, the rest will be completely intact.

-- 
With respect,
Roman

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Re: Raid0 and drive failure.

[Henti Smith]

On Sat, Sep 17, 2011 at 5:05 PM, Roman Mamedov <rm@romanrm.ru> wrote:
> On Sat, 17 Sep 2011 16:10:44 +0200
> Henti Smith <henti@geekware.co.za> wrote:
>
>> At it's core I'm looking for a way to do something similar windows
>> drive extender that allows you to pool your drives without loosing all
>> your data when one drive is lost.
>
> Use mhddfs: http://romanrm.ru/en/mhddfs
> Only one drive's files are lost when that drive fails, the rest will be completely intact.

Thank you very much, this looks exactly like what I was looking for. I
will play more with this.

Regards
Henti