[linux-lvm] Solving the "metadata too large for circular buffer" condition
Ray Morris
support at bettercgi.com
Wed Nov 24 23:07:57 UTC 2010
Taking another look, my estimate of required metadatasize
might be off by a factor of five or so. 128K might be sufficient
for 100 LVs, depending on fragmentation and such.
Still, the history of computer science is largely a story
of problems caused by people thinking they'd allocated plenty
of space. Today you can't fdisk a drive or array larger than
2TB because someone thought 32 bits would plenty. Probably
best to allocate 100 times as much as you think you'll ever
need - a few MB of disk space is cheap.
--
Ray Morris
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On 11/24/2010 02:28:11 PM, Andrew Gideon wrote:
>
> We've just hit this error, and it is blocking any expansion of
> existing
> or creation of new volumes.
>
> We found:
>
> http://readlist.com/lists/redhat.com/linux-lvm/0/2839.html
>
> which appears to describe a solution. I'm doing some reading, and
> I've
> set up a test environment to try things out (before doing anything
> risky
> to production). But I'm hoping a post here can save some time (and
> angst).
>
> First: The referenced thread is two years old. I don't suppose
> there's a
> better way to solve this problem today?
>
> Assuming not...
>
> I'm not sure how metadata is stored. It seems like, by default, it is
> duplicated on each PV. I'm guessing this because one can't just add
> new
> PVs (with larger metadatasize values), but one must also remove the
> old
> metadata. Is that right?
>
> Are there are consequences to removing the metadata from most of the
> physical volumes? I've six, so I'd be adding a seventh and eighth
> (two
> for redundancy, though the PVs are all built on RAID sets).
>
> The "pvcreate --restorefile ... --uuid ... --metadatacopies 0" command
> would be executed on the existing 6 physical volumes? No data would
> be
> lost? I want to be *very* sure of this (so I'm not trashing an
> existing
> PV).
>
> What is the default metadatasize? Judging from lvm.conf, it may be
> 255.
> 255 Megabytes? Is there some way to guestimate how much space I
> should
> expect to be using? I thought perhaps pvdata would help, but this is
> apparently LVMv1 only.
>
> [Unfortunately, 'lvm dumpconfig' isn't listing any data in the
> metadata
> block.]
>
> There's also mention in the cited thread of reducing fragmentation
> using
> pvmove. How would that work? From what I can see, pvmove will move
> segments. But even if two segments are moved from dislocated
> locations
> to immediately adjacent locations, I see nothing which says that these
> two segments would be combined into a single segment. So I'm not
> clear
> how fragmentation can be reduced.
>
> Finally, there was mention of changing lvm.conf - presumably,
> metadata.dirs - to help make more space. Once lvm.conf is changed,
> how
> is that change made live? Is a complete reboot required, or is there
> a
> quicker way?
>
> Thanks for any and all help...
>
> Andrew
>
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>
>
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