[linux-lvm] raid10 to raid what? - convert

[linux-lvm] raid10 to raid what? - convert

[lejeczek]

hi everyone

I'm sroogling and reading but before spend whole day doing 
that, I was hoping you guys, gals, done conversion from raid10?

I'm thinking best(natural?) would be to convert to two raid0 
LVs, right. Am I right? Would it be optimal, and how do you 
do it?

many thanks, L.

Re: [linux-lvm] raid10 to raid what? - convert

[John Stoffel]

lejeczek> I'm sroogling and reading but before spend whole day doing
lejeczek> that, I was hoping you guys, gals, done conversion from
lejeczek> raid10?

Please post your configuration and explain what you're trying to do in
more detail.

lejeczek> I'm thinking best(natural?) would be to convert to two raid0
lejeczek> LVs, right. Am I right? Would it be optimal, and how do you
lejeczek> do it?

You don't put LVs directly ontop of RAID0, you put them in VGs, which
reside in PVs, which reside on disks or RAIDs, or iSCSI LUNs, etc.

It sounds like you have two filesystems, each in their own LV.  You
want to move them off a RAID10 (four disks, in two mirrored PAIRS,
stripped across them is what I assume), because why?

Give more details.  You do realize that while you will gain space, you
will lose reliability with RAID0, if one disk fails, all your data is
gone.

John

Re: [linux-lvm] raid10 to raid what? - convert

[lejeczek]

On 16/10/17 22:16, John Stoffel wrote:
> lejeczek> I'm sroogling and reading but before spend whole day doing
> lejeczek> that, I was hoping you guys, gals, done conversion from
> lejeczek> raid10?
>
> Please post your configuration and explain what you're trying to do in
> more detail.
>
> lejeczek> I'm thinking best(natural?) would be to convert to two raid0
> lejeczek> LVs, right. Am I right? Would it be optimal, and how do you
> lejeczek> do it?
>
> You don't put LVs directly ontop of RAID0, you put them in VGs, which
> reside in PVs, which reside on disks or RAIDs, or iSCSI LUNs, etc.
>
> It sounds like you have two filesystems, each in their own LV.  You
> want to move them off a RAID10 (four disks, in two mirrored PAIRS,
> stripped across them is what I assume), because why?
>
> Give more details.  You do realize that while you will gain space, you
> will lose reliability with RAID0, if one disk fails, all your data is
> gone.
>
> John
no other raids but LVM's own.
not much in configuration, unless I misunderstand, question 
I'm posing is simple - is it possible to convert/split lvm 
raid10 LV into two raid0 LVs? (here one thing comes to mind: 
data stays intact?) Or raid10 LV to any other raid?

As I sroogled I saw there is "mirror spitting" but term 
raid10 does not appear in that context, or I failed to find it.

But man pages also mention, with regards to raid takeover:
"..
        ·  between striped/raid0 and raid10.
..."
So it sounds like possible(so no other raid levels but these 
two), only might be intricate process/procedure, which is 
not documented, or again, I failed to find it.


>
> _______________________________________________
> linux-lvm mailing list
> linux-lvm@redhat.com
> https://www.redhat.com/mailman/listinfo/linux-lvm
> read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/

Re: [linux-lvm] raid10 to raid what? - convert

[Stuart D. Gathman]

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You still haven't said what you are trying to accomplish.  I wouldn't
have bothered responding to such a vague question until you provided
some tantalizing clues.  Until your lastest clues, I would have advised
using rsync or dd to copy your data to a new volume.  But now it sounds
like you ran out of budget for another disk, or need to minimize down
time, and want to reconfigure in place.

First off, raid10 is a linux specialty (I didn't know LVM supported it,
thanks!), and is not the same as raid1+0 (raid1 on top of raid0).
However, your previous clue tells us that probably you have at least 4
disks in your raid10.  So you should be able to remove 2 legs from the
raid10, and still have the equivalent of a raid0.  But this is not
certain as raid10 works perfectly well with 2 or 3 disks, including the
redundancy.  In any case, you can remove at least 1 leg from your
raid10.  Be sure to backup first in any case.

Now that you've cut the disk used in half (and your data is precariously
dependent on the health of *both* underlying physical disks), what did
you want to do next?  Maybe you just want to create a different kind of
raid with the released space and do that rsync or dd?

On Tue, 17 Oct 2017, lejeczek wrote:

> no other raids but LVM's own.
> not much in configuration, unless I misunderstand, question I'm posing is 
> simple - is it possible to convert/split lvm raid10 LV into two raid0 LVs? 
> (here one thing comes to mind: data stays intact?) Or raid10 LV to any other 
> raid?
>
> As I sroogled I saw there is "mirror spitting" but term raid10 does not 
> appear in that context, or I failed to find it.
>
> But man pages also mention, with regards to raid takeover:
> "..
>        ·  between striped/raid0 and raid10.
> ..."
> So it sounds like possible(so no other raid levels but these two), only might 
> be intricate process/procedure, which is not documented, or again, I failed 
> to find it.

-- 
 	      Stuart D. Gathman <stuart@gathman.org>
"Confutatis maledictis, flamis acribus addictis" - background song for
a Microsoft sponsored "Where do you want to go from here?" commercial.

Re: [linux-lvm] raid10 to raid what? - convert

[Stuart D. Gathman]

On Tue, 17 Oct 2017, Stuart D. Gathman wrote:

> thanks!), and is not the same as raid1+0 (raid1 on top of raid0).

Sorry, that is raid0 on top of raid1.  With raid1 on top, then after
the first disk failure, the second failure has a 66% chance of
destroying the data.  With raid0 on top, the second failure has only
a 33% chance of destroying the data.

Raid10 is a way of striping the data with redundancy in a single layer.

-- 
 	      Stuart D. Gathman <stuart@gathman.org>
"Confutatis maledictis, flamis acribus addictis" - background song for
a Microsoft sponsored "Where do you want to go from here?" commercial.

Re: [linux-lvm] raid10 to raid what? - convert

[Tanstaafl]

On 10/17/2017, 4:57:10 PM, Stuart D. Gathman <stuart@gathman.org> wrote:
> First off, raid10 is a linux specialty (I didn't know LVM supported it,
> thanks!),

Eh? Not sure what you mean by that, RAID10 is used by many hardware RAID
controllers, so is certainly not some kind of esoteric linux
'specialty', unless I misunderstood.

I've been using RAID10 exclusively for over 10 years ever since I
narrowly avoided a major catastrophe with RAID5.

> and is not the same as raid1+0 (raid1 on top of raid0).

Not according to everything I've ever read about it... for example:

http://www.thegeekstuff.com/2011/10/raid10-vs-raid01

> But this is not certain as raid10 works perfectly well with 2 or 3
> disks, including the redundancy.
You must be talking about something else... RAID10 requires at least 4
disks, and always an even number, although most RAID controllers support
the designation of at least one hot spare (so it will auto-rebuild using
the hot spare in the event of a failure). Been using this configuration
in my 5 drive QNAP NAS's for along time.

Re: [linux-lvm] raid10 to raid what? - convert

[Stuart D. Gathman]

On Wed, 18 Oct 2017, Tanstaafl wrote:

>
>> and is not the same as raid1+0 (raid1 on top of raid0).
>
> Not according to everything I've ever read about it... for example:

https://en.wikipedia.org/wiki/Non-standard_RAID_levels#Linux_MD_RAID_10

>> But this is not certain as raid10 works perfectly well with 2 or 3
>> disks, including the redundancy.
> You must be talking about something else... RAID10 requires at least 4
> disks, and always an even number, although most RAID controllers support
> the designation of at least one hot spare (so it will auto-rebuild using
> the hot spare in the event of a failure). Been using this configuration
> in my 5 drive QNAP NAS's for along time.

Yep.  Not talking about raid1+0

Linux raid10 really ought to be a "standard" - and effectively is.
I use it whenever I can (with only 2 disks I use raid1 so I can alias
the legs as non-raid).

-- 
 	      Stuart D. Gathman <stuart@gathman.org>
"Confutatis maledictis, flamis acribus addictis" - background song for
a Microsoft sponsored "Where do you want to go from here?" commercial.

Re: [linux-lvm] raid10 to raid what? - convert

[lejeczek]

On 17/10/17 21:57, Stuart D. Gathman wrote:
> You still haven't said what you are trying to accomplish.  
> I wouldn't
> have bothered responding to such a vague question until 
> you provided
> some tantalizing clues.  Until your lastest clues, I would 
> have advised
> using rsync or dd to copy your data to a new volume.  But 
> now it sounds
> like you ran out of budget for another disk, or need to 
> minimize down
> time, and want to reconfigure in place.
>

gee, with this much enthusiasm I can imagine you solve many 
problems, however I can also imagine at the same time you 
create also problems that do not exists.
but honestly & truthfully appreciate this enthusiasm & help.

> First off, raid10 is a linux specialty (I didn't know LVM 
> supported it,
> thanks!), and is not the same as raid1+0 (raid1 on top of 
> raid0).
> However, your previous clue tells us that probably you 
> have at least 4
> disks in your raid10.  So you should be able to remove 2 
> legs from the
> raid10, and still have the equivalent of a raid0.  But 
> this is not
> certain as raid10 works perfectly well with 2 or 3 disks, 
> including the
> redundancy.  In any case, you can remove at least 1 leg 
> from your
> raid10.  Be sure to backup first in any case.
>
> Now that you've cut the disk used in half (and your data 
> is precariously
> dependent on the health of *both* underlying physical 
> disks), what did
> you want to do next?  Maybe you just want to create a 
> different kind of
> raid with the released space and do that rsync or dd?
>

I'm still looking for an answer - if it's possible then how 
to split raid10 into two raid0 LVs(with perhaps having data 
intact?)
I've been fiddling with --splitmirrors but either I got it 
wrong or I didn't and command just fails.
More than contemplating theories and general knowledge on 
raid I'd prise a lot succinct, concrete info, actuall 
experience of "howto".

But I shall now try my fiddling virtualized way, problem at 
hand I had, I had to solve different way completely.

> On Tue, 17 Oct 2017, lejeczek wrote:
>
>> no other raids but LVM's own.
>> not much in configuration, unless I misunderstand, 
>> question I'm posing is simple - is it possible to 
>> convert/split lvm raid10 LV into two raid0 LVs? (here one 
>> thing comes to mind: data stays intact?) Or raid10 LV to 
>> any other raid?
>>
>> As I sroogled I saw there is "mirror spitting" but term 
>> raid10 does not appear in that context, or I failed to 
>> find it.
>>
>> But man pages also mention, with regards to raid takeover:
>> "..
>>        ·  between striped/raid0 and raid10.
>> ..."
>> So it sounds like possible(so no other raid levels but 
>> these two), only might be intricate process/procedure, 
>> which is not documented, or again, I failed to find it.
>
>
>
> _______________________________________________
> linux-lvm mailing list
> linux-lvm@redhat.com
> https://www.redhat.com/mailman/listinfo/linux-lvm
> read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/

Re: [linux-lvm] raid10 to raid what? - convert

[John Stoffel]

>>>>> "lejeczek" == lejeczek  <peljasz@yahoo.co.uk> writes:

lejeczek> On 17/10/17 21:57, Stuart D. Gathman wrote:
>> You still haven't said what you are trying to accomplish.� 
>> I wouldn't
>> have bothered responding to such a vague question until 
>> you provided
>> some tantalizing clues.� Until your lastest clues, I would 
>> have advised
>> using rsync or dd to copy your data to a new volume.� But 
>> now it sounds
>> like you ran out of budget for another disk, or need to 
>> minimize down
>> time, and want to reconfigure in place.
>> 

lejeczek> gee, with this much enthusiasm I can imagine you solve many
lejeczek> problems, however I can also imagine at the same time you
lejeczek> create also problems that do not exists.  but honestly &
lejeczek> truthfully appreciate this enthusiasm & help.

Since you provided zero data on your configuration... what else do you expect?

>> First off, raid10 is a linux specialty (I didn't know LVM 
>> supported it,
>> thanks!), and is not the same as raid1+0 (raid1 on top of 
>> raid0).
>> However, your previous clue tells us that probably you 
>> have at least 4
>> disks in your raid10.� So you should be able to remove 2 
>> legs from the
>> raid10, and still have the equivalent of a raid0.� But 
>> this is not
>> certain as raid10 works perfectly well with 2 or 3 disks, 
>> including the
>> redundancy.� In any case, you can remove at least 1 leg 
>> from your
>> raid10.� Be sure to backup first in any case.
>> 
>> Now that you've cut the disk used in half (and your data 
>> is precariously
>> dependent on the health of *both* underlying physical 
>> disks), what did
>> you want to do next?� Maybe you just want to create a 
>> different kind of
>> raid with the released space and do that rsync or dd?
>> 

lejeczek> I'm still looking for an answer - if it's possible then how
lejeczek> to split raid10 into two raid0 LVs(with perhaps having data
lejeczek> intact?)  I've been fiddling with --splitmirrors but either
lejeczek> I got it wrong or I didn't and command just fails.  More
lejeczek> than contemplating theories and general knowledge on raid
lejeczek> I'd prise a lot succinct, concrete info, actuall experience
lejeczek> of "howto".

Have you tried setting up some /dev/loop# devices and re-creating your
setup on smaller devices and trying out various options?

It sounds like you want to take an existing RAID10, remove half the
disks (removing all redundancy) and then rebuilding into a new setup
so you can move the data over?

Even some simple examples of what you have and what you're trying to
accomplish without showing your array names, etc would be a big help.

lejeczek> But I shall now try my fiddling virtualized way, problem at
lejeczek> hand I had, I had to solve different way completely.

I can't make heads or tails of this.  Sorry.

Re: [linux-lvm] raid10 to raid what? - convert

[lejeczek]

On 18/10/17 21:46, John Stoffel wrote:
>>>>>> "lejeczek" == lejeczek  <peljasz@yahoo.co.uk> writes:
> lejeczek> On 17/10/17 21:57, Stuart D. Gathman wrote:
>>> You still haven't said what you are trying to accomplish.
>>> I wouldn't
>>> have bothered responding to such a vague question until
>>> you provided
>>> some tantalizing clues.  Until your lastest clues, I would
>>> have advised
>>> using rsync or dd to copy your data to a new volume.  But
>>> now it sounds
>>> like you ran out of budget for another disk, or need to
>>> minimize down
>>> time, and want to reconfigure in place.
>>>
> lejeczek> gee, with this much enthusiasm I can imagine you solve many
> lejeczek> problems, however I can also imagine at the same time you
> lejeczek> create also problems that do not exists.  but honestly &
> lejeczek> truthfully appreciate this enthusiasm & help.
>
> Since you provided zero data on your configuration... what else do you expect?
>
gee, I don't know... maybe... to look at the problem: 
split/conversion of lvm raid10 instead of ... you know

>>> First off, raid10 is a linux specialty (I didn't know LVM
>>> supported it,
>>> thanks!), and is not the same as raid1+0 (raid1 on top of
>>> raid0).
>>> However, your previous clue tells us that probably you
>>> have at least 4
>>> disks in your raid10.  So you should be able to remove 2
>>> legs from the
>>> raid10, and still have the equivalent of a raid0.  But
>>> this is not
>>> certain as raid10 works perfectly well with 2 or 3 disks,
>>> including the
>>> redundancy.  In any case, you can remove at least 1 leg
>>> from your
>>> raid10.  Be sure to backup first in any case.
>>>
>>> Now that you've cut the disk used in half (and your data
>>> is precariously
>>> dependent on the health of *both* underlying physical
>>> disks), what did
>>> you want to do next?  Maybe you just want to create a
>>> different kind of
>>> raid with the released space and do that rsync or dd?
>>>
> lejeczek> I'm still looking for an answer - if it's possible then how
> lejeczek> to split raid10 into two raid0 LVs(with perhaps having data
> lejeczek> intact?)  I've been fiddling with --splitmirrors but either
> lejeczek> I got it wrong or I didn't and command just fails.  More
> lejeczek> than contemplating theories and general knowledge on raid
> lejeczek> I'd prise a lot succinct, concrete info, actuall experience
> lejeczek> of "howto".
>
> Have you tried setting up some /dev/loop# devices and re-creating your
> setup on smaller devices and trying out various options?
>
> It sounds like you want to take an existing RAID10, remove half the
> disks (removing all redundancy) and then rebuilding into a new setup
> so you can move the data over?
>
> Even some simple examples of what you have and what you're trying to
> accomplish without showing your array names, etc would be a big help.
>
> lejeczek> But I shall now try my fiddling virtualized way, problem at
> lejeczek> hand I had, I had to solve different way completely.
>
> I can't make heads or tails of this.  Sorry.
in a virtual environment I'll try to reproduce the problem 
and carry on there.
If a can find any solution, or just anything helpfully 
informative I'll mail the list.


> _______________________________________________
> linux-lvm mailing list
> linux-lvm@redhat.com
> https://www.redhat.com/mailman/listinfo/linux-lvm
> read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/

Re: [linux-lvm] raid10 to raid what? - convert

[Xen]

lejeczek schreef op 18-10-2017 17:52:

> I'm still looking for an answer - if it's possible then how to split
> raid10 into two raid0 LVs(with perhaps having data intact?)
> I've been fiddling with --splitmirrors but either I got it wrong or I
> didn't and command just fails.
> More than contemplating theories and general knowledge on raid I'd
> prise a lot succinct, concrete info, actuall experience of "howto".

Sorry that I can't help you here, but I believe it is possible with 
mdraid.

However note that if you can spend the time you could take two disks, 
wipe them, put raid 0 on it, and then copy the still functioning RAID 10 
over. I know that's not what you're asking but personally I have no 
hands-on experience with LVM raid and metadata.

I assume that even if you were to manage to get a raid 0 going with pure 
DM commands you'd still need to change LVM's metadata and no clue how to 
do that myself.

Conceivably, copying your data over is not ideal but it should not take 
longer than a day?

Don't forget that RAID 10 is 2 stripes of mirrors...

But LVM typically prevents you to operate on a volume group if not all 
PVs are present...

Anyway if it can't be done by lvconvert, it probably can't be done 
(without whatever complex thing).