Matthias Apitz wrote:
> El día Thursday, December 08, 2011 a las 09:57:13AM -0600, Dan Nelson
> escribió:
>
> > Cheap USB thumb drives aren't really optimized for small random-I/O writes.
> > Can you try mounting the filesystem async? that might help a little. A
> > workaround would be to use mdconfig to create a block device (backed by
> > either swap or a file on your hard drive) the same size as your flash drive,
> > newfs and restore to that, then umount the filesystem and dd the raw image
> > directly to your flash drive.
>
> Hello Dan,
>
> Thanks for your hints. I tend to add that those USB thum drives aren't
> good for anything. I have a certain number of them containing each a
> complete bootable FreeBSD (including 'src', 'obj' and binary packages)
> to install my laptops and netbooks from them;
>
> after some time these USB keys tend to loose data:
> files are corrupt a bit, dirs are missing and so on; that's
> why I wanted to make dump(8) nackups of them, to restore them from time
> to time; I will drop the idea and will just make dd(1) backups of the
> full /dev/da0;
Additional to all the other good points others wrote earlier,
may I mention: ...
I've found some sticks are slower than others.
Sometimes I do a performance & integrity test with my
http://berklix.com/~jhs/src/bsd/jhs/bin/public/testblock
One (free promo) stick I found lies, see this comment in my
http://berklix.com/~jhs/src/bsd/fixes/FreeBSD/src/jhs/etc/devd/jhs.conf
# The end of it is write only memory !
# It lets one write the last chunck,
# It even lets one read that last chunk,
# but the content of the last chunck is all zeroes.
Another 2G stick was particularly slow: (marked as) Sony,
bought at a computer Sunday 'flea' market in Croydon England,
in retrospect I wonder if manufacturer Sony might have withdrawn them
from sale, marked the batch for destruction, & possibly some criminal
'liberated' them for resale again ?
(Such things do happen, eg In Germany years back, pre USB
era, CT Mag reported reported Betruger/Placebo cache chips.
They were just ceramic with no silicon in, it was reported
importers (in Munich I think) were afraid to sue chinese
exporters, fear of Triads! maybe last bit was speculation,
but wan't My speculation, I read it, whatever, can't remember
more now)
Block Sizes:
Maybe USB sticks may have different size/ speed front end
cache chips on USB sticks ? Hans would know I suppose. ?
Apart from soft updates, one can also choose the block sizes
newfs creates, I recall FFS is larger than UFS ?.
Maybe we should send-pr some suggested size for man newfs
if targeting images for USB sticks.
(is that a question to consider jointly with fs@ list ? )
Voltages:
I've recently been bitten by appalling problems on a bunch
of 2 of my externals discs, using 2 different laptops, 2/3
hubs, & 3 power supplies. Various combinations come back
to bad voltage regulation, usually too low, some too high.
But I assume discs will be more susceptible than sticks.
However next time a motherboard fails for any of you, I
suggest don't discard, first hacksaw off the double USB socket,
solder wires across, add extra wires for a meter, so you
can monitor voltage & current.
Mastering first on hard disc (per Dan's suggestion, mdconfig etc)
is a good idea, I was considering this earlier when building
a new stick/ extended Live-FS. .. using mdconfig etc,
but it's heavy & slow after the initial image create, to keep
rewriting, even if at large dd bs=
So I use incremental writes
I keep personal backups & bins & Live FS & mp3 to play etc
all on USB sticks. Still usable though 'cos I rarely change
too much at one time. & rdist6 updates what's changed.
(would also correct odd corruption Matthias)
I even sue gbde encrypted FS (ie more performance degradation)
.. and updates still happens acceptably if not exactly fast.
Others could use rsync if they dont fancy rdist6.
Cheers,
Julian
--
Julian Stacey, BSD Unix Linux C Sys Eng Consultants Munich http://berklix.com
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