At Tue, 20 Jan 2026 10:20:54 +0100, Hauke Fath <[email protected]> wrote: Subject: Re: Xen storage for NetBSD guests: performance vs. consistent backups (sanity check) > > On Mon, 19 Jan 2026 21:15:17 +0100, Matthias Petermann wrote: > > Unfortunately, once LVM enters the picture, I have repeatedly run > > into situations where triggering an FSS snapshot causes severe stalls > > or complete lockups. > > This is on which version? > > I am asking because I have been running ffs snapshot backups (TSM here) > on netbsd-9 DomUs for years without ever running into any issues..
I'm very surprised that LVM could play any part in causing stalls or
lock-ups.
That being said I've never tried making FFS snapshots in any of my
NetBSD my domUs. (I just use rsync from the live filesystem as I don't
have any important applications that continue to modify files all night
long.) (Also the terminology used around ffsconfig(8) makes me
uncomfortable and makes me think I don't actually understand what it
all means -- it all seems backwards to me.)
It would be really interesting, and perhaps even important for us LVM
users, to try to track this down. If there's a simple recipe that can
reproduce such stalls or hangs that would be very useful!
In any case I've been using LVM LVs in my dom0s to host raw partitions
for domUs since day one of using Xen, so since NetBSD-5 I think. I find
them to be the most performant and, perhaps more importantly, the most
flexible solution overall. I can easily extend an LVM if more space is
necessary somewhere and then just resize the FFS for the domU, and
they're very easy to configure and manipulate at any time.
I too had once thought of using CCD volumes, but they have far too many
limitations vs LVM; and having had lots of previous experience using the
same kind of LVM on AIX in a past job I realized that in combination
with good hardware RAID, well LVM was just the most obvious possible
choice. I can take one giant raw partition provided by the RAID
controller and easily divide it up into as many LVs as necessary,
keeping any left over space available for expansion of any LV as
necessary.
That said I've not used ZFS on NetBSD yet. I find it too piggy for the
systems I currently have, especially since they already have high-end
hardware RAID controllers that do caching and proactive scanning for bad
sectors -- maybe I can try it on a next generation of machines, though
those to will have even better hardware RAID and it just doesn't make
sense to me to run ZFS on top of high-end hardware RAID -- a layer too
many (though the compression features of ZFS are intriguing -- that
would be a feature I would think to add to LVM though, along with
ZFS-like "dedup" and "copies" -- performance starts to get problematic
with any of those features though).
I presume ZFS "volumes" (zvols?) can be extended in size just as easily
as LVM LVs.
--
Greg A. Woods <[email protected]>
Kelowna, BC +1 250 762-7675 RoboHack <[email protected]>
Planix, Inc. <[email protected]> Avoncote Farms <[email protected]>
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