About Installing on USB memory stick

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About Installing on USB memory stick

Postby morgano » Feb 21st, '13, 19:15

1) I thought it would be nice to have a mageia to bring with me easily.
2) I have a relative who have problem with windows, and earlier did not grook mandriva to manage it herself. If the system is on a USB it can easily be mailed to me for system maintenance/upgrade/repair/whatever.

Anyhow i simply installed mgs3b2 on a Sandisk Extreme 32 GB USB stick - working great.

Now i need to make sure it do not wear out. Could not find any info by retailer nor sandisk web site, so i mailed them and they responded cryptically that as this is a end user product the cannot supply wear leveling technology or datasheet.
Oh whell then we buy transcend which use dynamical wear levelling: http://www.transcendusa.com/support/dlc ... GJF700.pdf
Another manufacturers repś reply: http://forums.anandtech.com/showpost.ph ... ostcount=5

Then there is the question of TRIM support to make wear leveling work better.
an idea here is to reserve unpartitioned space to ensure head room for wear levelling
http://forums.anandtech.com/showpost.ph ... stcount=14

Best would be if the controller support TRIM.
I see no reason for why not implementing an already developed technology. Should not depend on wether the interface is USB or SATA.

For a "seroius" install, best is probably to use a good tool to format it intelligently and align the filesystem
http://superuser.com/questions/379074/h ... ose-consid

Then there is the question of what filesystem to use. ext4 use space more efficiently. Journal cause wear but saves from other problems.

Summing up:

1) Chose drive that use wear levelling. Possilby that undertsand TRIM (And make sure the system use it)
2) choose filesystem and variant/mode i.e ext4 and i prefer journalled (more wear and delay on the stick but survives other errors system hangs better)
3) format, includning align filesystem. Do not forget swap even if you paln not to use it.

Another option would be to use a CF card (actually thinner so even easier to send by post) but need a relatively clumsy USB interface (if the computer do not have PC-card slot or similar for FS reader)
But still the questions are the same. Or possibly worse: CF-card is IDE? so it can by specification not support TRIM?

Anyone have any other input?
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Re: About Installing on USB memory stick

Postby doktor5000 » Feb 21st, '13, 21:00

Use an mSATA SSD? Use a second-hand SSD in an external enclosure?

You may also want to look at the first generation of netbooks (e.g. EEE pc or Acer One) whose owners
often used CF/SD cards to extend space or install additional operating system. They mostly used
ext2 as the journal and all that extended ext3/4 attributes come with quite an overhead regarding writes.

Also most el-cheapo flash drives are probably the worst candidates for such an experiment, either try
with a quality flash drive (which costs nearly as much as a cheap small SSD).
For example i've just seen a ~30$ SSD from Super Talent with 16GB, or a 32GB for ~40$
which fits into the miniPCIE-slot of EEE pc's.

You may also want to look at http://forums.anandtech.com/showthread.php?t=2079571
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Re: About Installing on USB memory stick

Postby morgano » Feb 22nd, '13, 01:21

Yes that was the thread i also referenced above.
I have also looked a bit in thread on Raspberry PI where they had problems with CF card.
What hurts is that most manufacturers of both CF and USB flash drives hide important informations.
Competition seem to be only about presentation and design.
Cost do not matter much, the Sandisk Extreme i test on is not cheap but nowhere can info be found. yet.
And though it is intended to be carried the do not even protect the PCB with coating of any kind. Crap. I had to get rid of the clumsy shell of Sandisk Extreme to even be able to plug it in the same time as another device in my laptop and i protected it with schrink tube. It is very thin. It just lack a *thin* sturdy shell and any moisture protection, and documentation...
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Re: About Installing on USB memory stick

Postby doktor5000 » Feb 22nd, '13, 12:40

Mostly all vendors will not provide detailed documentation for flash drives, that's it. They are just made out of cheap flash cells mostly with a simple controller.
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Re: About Installing on USB memory stick

Postby morgano » Feb 22nd, '13, 14:19

I believe the difference is only some failed business strategic plan.
The difference between SSD and USB use, is USB need be more robust, but store less.
There is no reason to not deploy error correction, wear leveling, etc in the USB. Especially for a company that already have proven technology in existing products.
On the contrary, deploying a capable controller make using more compact and more error prone flash memory, in total saving silicon area and cost.
I believe all major players do some of this, it is just not expressed publicly because they are afraid people will be scared of it looking too complex.
And they may be right in that.

But anyhow when the USB can write new data somewhere before discarding and erasing the old content then it is much faster - makes a selling point for speed, or they can use slower cheaper flash.
That technology is called dynamic wear leveling. And of course there need be some error correction/detection/swapping away bad memory areas. Then there is not very much more logic needed to do static wear leveling, meaning also static data are moved around so the area where there have been static data gets worn by dynamic data, ans historically static data stored on more worn places.
http://en.wikipedia.org/wiki/Wear_leveling

EDIT: according to this document page 5 some USB sticks use dynamic and other static wear leveling http://www.usenix.org/event/fast10/tech ... oboila.pdf
Should be even more advanced these days.

Product alternative: Transcend have "Endurance" group of USB memory, and inthat the jetflash 170 series that use SLC. Expensive per size but high write speed and probably endures more writes. But 8 GB is a bit low for full system+data+swap. It would be good if manufacturers state how many terabytes can be written before they risk fail. But having them tag any USB as "Endurance" is better than nothing...

Interesting read: http://forum.embeddedarm.com/showthread ... rance-test There seem to be a trend that even the simple sturdier "Industrial" memory products get smarter controllers for bad and for worse. But "all" have http://superuser.com/questions/17350/wh ... -card?lq=1

People want to buy a tiny thing they can plug in and use, ant the only data they want to read is that is is MS compatible, size, cost and have a fancy name.
Some have problem to not plug in USB upside down...
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