Re: SSD Optimizations

[Gordan Bobic <gordan@bobich.net>]

On Thu, 11 Mar 2010 12:31:03 +0100, Stephan von Krawczynski
<skraw@ithnet.com> wrote:
>> > > >On Wed, Mar 10, 2010 at 11:49 AM, Gordan Bobic <gordan@bobich.net>
>> > > >wrote:
>> > > >>Are there options available comparable to ext2/ext3 to help
reduce
>> > > >>wear and improve performance?
>> > 
>> > With SSDs you don't have to worry about wear.
>> 
>> Sorry, but you do have to worry about wear. I was able to destroy a
>> relatively
>> new SD card (2007 or early 2008) just by writing on the first 10MiB
over
>> and
>> over again for two or three days. The end of the card still works
>> without
>> problems but about 10 sectors on the beginning give write errors.
> 
> Sorry, the topic was SSD, not SD.

SD == SSD with an SD interface.

> SSDs have controllers that contain heavy
> closed magic to circumvent all kinds of troubles you get when using
> classical flash and SD cards.

There is absolutely no basis for thinking that SD cards don't contain wear
leveling logic. SD standard, and thus SD cards support a lot of fancy copy
protection capabilities, which means there is a lot of firmware involvement
on SD cards. It is unlikely that any reputable SD card manufacturer
wouldn't also build wear leveling logic into it.

> Honestly I would just drop the idea of an SSD option simply because the
> vendors implement all kinds of neat strategies in their devices. So in
the
> end you cannot really tell if the option does something constructive and
not
> destructive in combination with a SSD controller.

You can make an educated guess. For starters given that visible sector
sizes are not equal to FS block sizes, it means that FS block sizes can
straddle erase block boundaries without the flash controller, no matter how
fancy, being able to determine this. Thus, at the very least, aligning FS
structures so that they do not straddle erase block boundaries is useful in
ALL cases. Thinking otherwise is just sticking your head in the sand
because you cannot be bothered to think.

> Of course you may well discuss about an option for passive flash devices
> like ide-CF/SD or the like. There is no controller involved so your fs
> implementation may well work out.

I suggest you educate yourself on the nature of IDE and CF (which is just
IDE with a different connector). There most certainly are controllers
involved. The days when disks (mechanical or solid state) didn't integrate
controllers ended with MFM/RLL and ESDI disks some 20+ years ago.

Gordan