docs/177431: Handbook & Announcements recommend poor dd options for memstick images
Ronald F.Guilmette
rfg at tristatelogic.com
Thu Mar 28 03:50:01 UTC 2013
>Number: 177431
>Category: docs
>Synopsis: Handbook & Announcements recommend poor dd options for memstick images
>Confidential: no
>Severity: non-critical
>Priority: medium
>Responsible: freebsd-doc
>State: open
>Quarter:
>Keywords:
>Date-Required:
>Class: doc-bug
>Submitter-Id: current-users
>Arrival-Date: Thu Mar 28 03:50:00 UTC 2013
>Closed-Date:
>Last-Modified:
>Originator: Ronald F. Guilmette
>Release: FreeBSD 9.1-RELEASE amd64
>Organization:
entr0py
>Environment:
FreeBSD 9.1-RELEASE amd64
>Description:
The Handbook, as shown on this web page:
http://www.freebsd.org/doc/en/books/handbook/bsdinstall-pre.html
recommends dd'ing the desired (?) memstick.img file to a USB memory stick
using the following command:
# dd if=FreeBSD-9.0-RELEASE-i386-memstick.img of=/dev/da0 bs=64k
(Please note that the specific filename mentioned here is now out-of-date
relative to the most recent -RELEASE.)
So anyway, there appear to be two things wrong with the above recommended
dd command, to wit:
(1) the recommended dd block size of 64k is probably highly sub-optimal
for many/most/all modern USB flash drives. It is apparently difficult
to find a single (minimal) block size that will provide best per-
formance for all USB flash drives, however online sources suggest
that a 1 MiB block size should provide excelent performance for
most such drives (and with relatively little waste of space).
(2) The dd command should probably also include the conv=sync option,
just as shown in the 9.1 RELEASE Announcement. (Otherwise it is
not 100% clear what will happen to the last few blocks of the
memstick.img file, i.e. the ones that don't fix neatly into exactly
`N' of the dd blocks.)
Separately and additionally, various versions of the official FreeBSD Release
Announcements, for example the version found here:
http://www.freebsd.org/releases/9.1R/announce.html
recommend using bs=10240 when dd'ing a memstick.img file to a USB flash
device. As noted above, this value is also probably highly sub-optimal,
and should probably be replaced (in *all* current and past Release
Announcement pages) to the value "bs=1M".
>How-To-Repeat:
Visit the two URLs mentioned above.
>Fix:
See above.
>Release-Note:
>Audit-Trail:
>Unformatted:
More information about the freebsd-doc
mailing list