Re: port-amd64/57266: Poor disk performance on VirtualBox vioscsi0 and NetBSD 10.0_BETA

[Robert Elz <kre%munnari.OZ.AU@localhost>]

The following reply was made to PR port-amd64/57266; it has been noted by GNATS.

From: Robert Elz <kre%munnari.OZ.AU@localhost>
To: Bartek Krawczyk <bbartlomiej.mail%gmail.com@localhost>
Cc: gnats-bugs%netbsd.org@localhost, port-amd64-maintainer%netbsd.org@localhost,
        netbsd-bugs%netbsd.org@localhost
Subject: Re: port-amd64/57266: Poor disk performance on VirtualBox vioscsi0 and NetBSD 10.0_BETA
Date: Sun, 12 Mar 2023 20:00:16 +0700

     Date:        Sun, 12 Mar 2023 11:31:54 +0100
     From:        Bartek Krawczyk <bbartlomiej.mail%gmail.com@localhost>
     Message-ID:  <1326a107-6fbd-27df-c0d6-b7dd69fceddb%gmail.com@localhost>
 
   | In general this is purely default NetBSD 10.0_BETA installation. The 
   | only options I changed is adding log, async and noatime to / mount in 
   | the installer.
 
 That's a combination that makes no sense, and I thought had been made
 impossible, but you seem to have achieved it.
 
 "async" says "just do all I/O to buffers, in any order, write to the
 disc when necessary, in any order, filesystem consistency if the system
 shoukd crash before umount is not guaranteed, and is often a complete
 disaster".  I use that a lot for trash fikesystems I can just newfs if
 needed, but want to run as fast as possible - like /usr/obj.  I also use
 it for src/pkgsrc while unpacking as I can always newfs and start again
 if something goes wrong.   I'd never recommend it for root though.
 
 "log" delays meta-data writes, but keeps track of what should be done
 and in what order so the filesystem can be made consistent after a crash.
 
 Using neither causes meta-data to be written synchronously, and in order,
 so the filesystem should never become inconsistent.  Safe, but slow,
 particularly for things like unpacking pkgsrc, which is almost all meta-data
 operations (allocating inodes, making new directory entries, ...)
 
 Async and log are almost opposites in intent, both make the filesystem
 do meta-data ops faster than the default, but in dramatically different
 ways.  It is possible the system is simply ignoring both of them, and
 operating in safe slow mode.   If not, then almost anything might be
 happening internally.   Just don't do that.
 
 For root just use log.  Not async.   If you use a separate filesystem
 for pkgsrc, you can mount that async while unpacking.  That is then lots
 faster.  After the unpack is done, umount and mount again without async
 (you can use log, or not, as you like - once unpacked, pkgsrc should
 get few future changes, just perhaps occasional updates, so it doesn't
 make a lot of difference - put the work directories elsewhere.)
 
 kre
 
 ps: the noatime option is immaterial to all of this.