[OLPC-AU] Golden image restores for laptops in shared use scenarios

James Cameron quozl at laptop.org
Tue Jan 18 03:18:19 EST 2011


On Tue, Jan 18, 2011 at 05:57:28PM +1100, Sridhar Dhanapalan wrote:
> Just so I understand this right, this is (in layman's terms) like a
> quick NANDblaster? That is, it can do multiple XOs at a time and it
> wipes any customisations and data that they may have?

Yes.

But with conditions.  Don't use it for an upgrade.

The technique relies on there being insignificant difference between the
pristine installed laptop and the target laptop.  It outperforms
NANDblaster and fs-update when restoring to the same operating system
build, since it is effectively only deleting files in /home/olpc and
undoing some first-boot changes in /etc/ and /var/ (using rsync
--delete).

It badly underperforms when trying to use it for operating system
upgrades, because that kind of change is extensive, and the process
writing to the internal storage becomes the critical path.

As an example, os852 to os860 has taken two hours so far, and netstat
shows a large socket receive queue for the rsync process on the target
laptop.  /proc/meminfo and /proc/diskstats shows the random write
pattern to the internal SD is the cause of the slowdown; there's a long
I/O queue to mmcblk0p2.  The wireless is mostly idle, only 777 MB
transmitted during that two hours.

> I'm just wondering how it could relate to our Mini Server project,
> which is designed for upgrading. I was planning on making an
> announcement about it this week, but here goes anyway:
> https://dev.laptop.org.au/projects/mini-server/wiki

olpc-update can be run automatically in the background using
olpc-update-query, while the laptop is in use by a learner, and so the
limited random write rate of the internal SD card will be less of an
issue.  Otherwise it should experience roughly the same delays.

You'll find that a batch of XO-1.5 doing an olpc-update from your server
will mostly be waiting for internal SD card writes to complete.

The same will be apparent using olpc-update with a .usb file.

-- 
James Cameron
http://quozl.linux.org.au/


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