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).


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

[John Stoffel]

> "lejeczek" == lejeczek   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.

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Re: [linux-lvm] lvm raid: pvmove vs lvconvert

[lejeczek]

On 18/10/17 15:42, lejeczek wrote:

hi there

in lvm raid LVs, which one should be used and how do they 
differ - would you know? Are they meant for different things?


sorry, I'm thinking specifically of: lvconvert --replace VS 
pvmove



many thanks, L.


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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 
"Confutatis maledictis, flamis acribus addictis" - background song for
a Microsoft sponsored "Where do you want to go from here?" commercial.

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