[schilytools] star hangs randomly during copy from ZFS to ZFS

[Greg A. Woods]

At Tue, 05 Nov 2024 00:01:56 +0100, Lasse Kliemann <lasse at lassekliemann.de> wrote:
Subject: Re: [schilytools] star hangs randomly during copy from ZFS to ZFS
>
> I can reproduce the issue, simply because it happens every time that I
> start the copy process. It does not happen at the same file or after
> the same amount of bytes copied though; this varies a lot - sometimes
> a few hundred GB, sometimes 1-2 TB.

A hang sounds far more like an OS (i.e. kernel) issue than a userland
issue.  You need to do "ps lx" to see the WCHAN column, and you might
want to run "fstat -p" against the process as well.

I would bet the problem is with ZFS, perhaps exacerbated by the way star
does I/O (vs., say, how other similar tools do I/O, e.g. in the sizes of
transactions).  You're copying a lot of data!

ZFS is known to suffer weird problems when it gets pushed to any limits
that might exist in a given system.

One of the things ZFS stresses the most in a system is memory.  If it
gets anywhere near running out of memory, perceived or otherwise, it
will get stuck.  How much memory does your machine have?  I don't know
enough about ZFS to know for sure how much memory a system might need to
have in order to effectively deal with shuffling around such large
amounts of data, but I'll bet it wants a lot!  One rule of thumb that's
often repeated, but perhaps not so oftenly justified, is 1GB RAM per TB
of disk, and that's just for the ZFS requirements alone -- everything
else you run, including the rest of the kernel, will add up to more RAM.

--
					Greg A. Woods <gwoods at acm.org>

Kelowna, BC     +1 250 762-7675           RoboHack <woods at robohack.ca>
Planix, Inc. <woods at planix.com>     Avoncote Farms <woods at avoncote.ca>
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