Date: Wed, 27 Mar 2013 20:42:04 -0700 (PDT) From: "Ronald F.Guilmette" <rfg@tristatelogic.com> To: FreeBSD-gnats-submit@freebsd.org Cc: rfg@tristatelogic.com Subject: docs/177431: Handbook & Announcements recommend poor dd options for memstick images Message-ID: <20130328034204.18BE73B3F7@segfault.tristatelogic.com> Resent-Message-ID: <201303280350.r2S3o0Ls063159@freefall.freebsd.org>
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>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of=/dev/da0 bs=64k (Please note that the specific filename mentioned here is now out-of-date relative to the most recent -RELEASE.)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:
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