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Re: install/50033: WABPL(4) is not enabled by default in sysinst(8)
The following reply was made to PR install/50033; it has been noted by GNATS.
From: David Holland <dholland-bugs%netbsd.org@localhost>
Subject: Re: install/50033: WABPL(4) is not enabled by default in sysinst(8)
Date: Sun, 6 Sep 2015 00:33:10 +0000
On Sat, Jul 04, 2015 at 02:40:01PM +0000, Martin Husemann wrote:
> Thanks for the PR, indeed releng/core should discuss and document the
> default for -7 ASAP.
...yes, since while it has problems, without it things are really
slow and still have problems.
> But just for documentation purposes, let me point out (from my personal
> memory/understanding) a few things:
> - There have been a few stability issues attributed to wapbl. I think they
> have been fixed (either in wapbl or the underlying disk drivers). These
> were probably the main reason hinted as "far too dangerous" in the
> disabling commit
I don't think so - I think that was about file data blocks. Anyway,
while there have been intermittent problems (50159 apparently being
one) it's not clear to me that there's any more trouble than with
> - There is the still open issue with deleting a large file taking
> ages and blocking the kernel completely during that time
Yes, plus the related issue that panics instead.
> - There are (depending on hardware) serious performance issues that
> can be avoided by setting vfs.wapbl.flush_disk_cache=0 (but that
> is not safe if there is no external UPS or the machine is a notebook)
Is there a PR specifically on this? I don't remember one, and it would
be good to collect up the information somewhere.
> - There is a (I would call it nearly phillosophical) issue with
> wapbl not being a full log file system (but only meta data is loged),
> so on crashes you may lose all contents of recently touched files -
> often showing up as a "cvs update" running while the system paniced
> leaving many 0 sized or truncated files around.
This I think was the motivation for turning it off; but remember that
ffs-without-wapbl has the same problem. It just runs slower and
therefore leaves you with fewer garbaged files...
David A. Holland
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