Feature #8438: Use /dev/rdisk instead of /dev/disk on manual install instructions for Mac

Feature #8438

Use /dev/rdisk instead of /dev/disk on manual install instructions for Mac

Added by emmapeel 2014-12-14 22:15:37 . Updated 2015-04-04 10:13:09 .

Status:

Resolved

Priority:

Elevated

Assignee:

Category:

Installation

Target version:

Tails_1.4

Start date:

2014-12-14

Due date:

% Done:

100%

Feature Branch:

bitingbird:doc/8438-mac_rdisk

Type of work:

End-user documentation

Blueprint:

Starter:

Affected tool:

Deliverable for:

Description

A user is suggesting to change the manual install instructions on Mac
to use /dev/rdisk instead of /dev/disk, as /dev/disk is a buffered
version of the former.

Anybody here knows about the risks of running dd on an unbuffered
device? User says /dev/rdisk is much faster, and you can use dd on the
raw device with no problems. On an Class 4 SD card the dd command run
around 20 times faster.

I am not aware of the intrincacies of Mac’s hardware. Does it makes
sense to investigate this further, provided is not used so often?

Subtasks

History

#1 Updated by sajolida 2014-12-16 13:40:26

Assignee set to emmapeel

Could you please:

- Ask this user when /dev/rdisk is available in all versions of Mac OS X (or whether it is something new).
- If the answer is not satisfactory, ask people on tails-testers to try that and report.

#2 Updated by emmapeel 2014-12-19 19:57:13

There are blog posts from 2008 about it, at least.

A lot of users in stackoverflow talk about 4 times quicker results using the dd command with /dev/rdisk

User suggests to at least suggest it on the documentation

#3 Updated by sajolida 2014-12-24 13:39:53

QA Check changed from Info Needed to Dev Needed

Ok, that sounds good. Do you feel like preparing a patch and have the new instructions validated by a Mac user?

#4 Updated by intrigeri 2015-01-15 15:42:55

Type of work changed from Test to End-user documentation

Seems to be a pretty good idea, especially once combined with bs=1M from what I’ve read (we’re using bs=16M on Linux, no idea why the Mac documentation currently doesn’t set any block size).

emmapeel, if you don’t think you’ll be working on this within, say, 3 months, please deassign this ticket from yourself so that others know that they can work on it :)

#5 Updated by sajolida 2015-02-04 22:47:11

With dd:

/dev/disk took 15 minutes to copy Tails 1.2.3 (through a USB hub)
/dev/rdisk took 76 minutes to copy Tails 1.2.3

So that didn’t work for me :(

#6 Updated by sajolida 2015-02-21 09:42:46

QA Check changed from Dev Needed to Info Needed

I tried again with the bs=16m option, and got something more interesting:

/dev/disk 250s
/dev/rdisk 165s

Still, seeing this I’m not sure that’s worth the trouble…

What do you think?

#7 Updated by intrigeri 2015-02-23 12:16:31

> Still, seeing this I’m not sure that’s worth the trouble…

Now that most, if not all, of the preparatory work has been done, it would feel a bit sad not to implement these improvement in the actual doc. Now, certainly it’s low priority, so don’t feel pressured to do it yourself and/or ASAP.