[linux-lvm] Re: Cannot create snapshots with kernel 2.4.24, lvm 1.0.4: Cannor allocate memory
Steve Kann
stevek at stevek.com
Wed Jan 21 18:51:02 UTC 2004
Hi List,
Thanks to some helpful off-list help from someone on the list, I've
found out that the trouble is related to using LVM with a HIMEM kernel.
I have rebuilt a new kernel without himem support, and snapshots are now
working.
On the other hand, if I run this way, I'll have 3GB of memory
basically sitting there doing not much else other than contributing to
chassis heat.
I also have to get the VFS-Lock patch in there (i'm building a
patched kernel now to test it) before snapshots are really useful.
So, does anyone either (a) know what the problem is, or (b) at least
know where I should look to try and fix it? I'm guessing that the
problem has been solved at least by some of the commerical distros..
Thanks.
-SteveK
Steve Kann wrote:
>
>
> Hi,
>
> I've seen some others on this (and other lists) who are having this
> problem, but I haven't been able to find a solution.
>
> I have a new box that I'd like to use with LVM. This will be a
> production fileserver. I've installed debian woody on it, and
> upgraded to the latest debian kernel, 2.4.24. I'm using the lvm 1.0.4
> tools.
>
> Naturally, I'm spending this time before this box is in use to play
> with LVM so I know how to do what I need to quickly before the fires
> hit. So, I've been able to happily create, grow, shrink, and remove
> lv's, as well as create and remove VGs and PVs.
>
> However, I cannot create a snapshot volume.
>
> This is pretty much why I wanted to use LVM in the first place
> (backing up a 400G active filesystem would be pretty impossible
> otherwise).
>
> The basic error I get is:
>
> 520 vgcreate -s 128M vg0 /dev/sda7
> 521 vgdisplay
> 522 lvcreate -L 256M -nhome vg0
>
> u2:~# lvcreate -s -L128M -c 4k -nhomesnap /dev/vg0/home
> lvcreate -- WARNING: the snapshot will be automatically disabled once
> it gets full
> lvcreate -- ERROR "Cannot allocate memory" creating VGDA for
> "/dev/vg0/homesnap" in kernel
>
> Other snapshot creation attempts, all of which fail the same way:
> 525 lvcreate -s -L1M -nhomesnap /dev/vg0/home
> 526 lvcreate -s -L128M -c 1M -nhomesnap /dev/vg0/home
>
>
> I've tried making a bunch of different volumes on which to base the
> snapshot, as well as a number of different parameters for the snapshot
> itself. I thought that perhaps it couldn't handle snapshots that were
> larger than a certain size, or snapshots of volumes that are beyond a
> certain size, etc.
>
> I should have plenty of memory:
> u2:~# free
> total used free shared buffers cached
> Mem: 4010744 111160 3899584 0 18444 58084
> -/+ buffers/cache: 34632 3976112
> Swap: 2097136 0 2097136
>
> If 3.8GB of Real, or 5.8 GB of virtual memory aren't actually enough
> to create a 128MB snapshot of a 256Mb volume (I tried making it very
> small!), then something must be very wrong!
>
> Any ideas?
>
>
>
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