Re: install/50033: WABPL(4) is not enabled by default in sysinst(8)

[Martin Husemann <martin%duskware.de@localhost>]

The following reply was made to PR install/50033; it has been noted by GNATS.

From: Martin Husemann <martin%duskware.de@localhost>
To: gnats-bugs%NetBSD.org@localhost
Cc: 
Subject: Re: install/50033: WABPL(4) is not enabled by default in sysinst(8)
Date: Sat, 4 Jul 2015 16:38:45 +0200

 Thanks for the PR, indeed releng/core should discuss and document the
 default for -7 ASAP.
 
 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
 
  - There is the still open issue with deleting a large file taking
    ages and blocking the kernel completely during that time
 
  - 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)
 
  - 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.
 
 Note that "log" can be enabled easily in sysinst, but in general giving
 options that are hard to explain and tough to decide at installation time
 is not good, so the default should be "ok for everyone".
 
 Martin