Re: [gentoo-user] [OT]: Optimal formatting a SDcard (64GB) with partions of diffent sizes and filesystems?

Mick <michaelkintzios@×××××.com> [15-08-07 20:04]:
> On Friday 07 Aug 2015 04:27:15 Fernando Rodriguez wrote:
> > On Thursday, August 06, 2015 6:18:59 PM Meino.Cramer@×××.de wrote:
> > > Hi,
> > >
> > > for my tablet PC I used a used 32GB FAT32 formatted SDcard. The
> > > formatting was already done by the manufacturer.
> > > Then I screwed it up and had to do the partioning and formatting
> > > myself again. "No big deal", I thought -- and was wrong.
> > > Yes, the "thing" I got could be read and written. But it was
> > > DAMN slow in comparison to the original formatting.
> > >
> > > I googled and found a description, which described exactly,
> > > what I wanted: An optimal formatting for one big FAT32 partion.
> > > I did it again ;) and: TADA! The speed was back.
> > > LINK:http://zero1-st.blogspot.de/2012/05/formatting-fat32-volumes-larger-> > than.html
> > >
> > > Now I need the something identical but explained in a way
> > > that it can be successfully applied to any partion layout
> > > and any SDcard size.
> > > Currently the new SDcard has 64GB (yes, the tablet eats that size
> > > well :) and needs at least two partions: One FAT32 and one ext4.
> > > May be that I need a different layout later.
> > >
> > > To what aspect and "logic" do I have to keep my eyes on, when
> > > it comes partioning/formatting any SDcard size with any partion
> > > layout and any filesystem?
> > >
> > > Thank you very much in advance for any help!
> > > Best regards,
> > > Meino
> >
> > I wrote a long reply to this and it appears to have been swallowed by
> > /dev/null.
> >
> > SD cards don't have 128K blocks. Except for the very early ones (standard
> > capacity), they are divided in allocation units (AU) that are 1MB to 4MB
> > for SDHC and even larger for SDXC. The only way to get that value is by
> > reading a register in the card (so you can't do it in usermode on linux).
> >
> > The AUs are divided into Recording Units (RUs). The size of these can be
> > deduced from the card speed class (that's the number inside the C on the
> > label), and the card capacity. For class 2 and 4 if the card is less than
> > 1GB it's 16KB, otherwise it's 32KB. For class 6 it is 64KB, and for class
> > 10 it's 512KB.
> >
> > After an AU is erased you can write to any of the free RUs in any order in
> > blocks of 512 bytes sequentially (the block size is configurable by the
> > driver but 512 is the most common). But if you write to a nonfree RU then
> > all non- free RU get copied to a new AU. So the performance hit depends on
> > how many non-free RUs are in the AU when this happens.
> >
> > So to get the best performance you need to align the first FAT cluster on
> > an AU boundary and that the RUs used by the reserved sectors after the FAT
> > are free. This is not so easy from usermode because you can't get the AU
> > size and you can't erase the AU to make sure reserved sectors are free.
> > The Windows 7 and later format utility will do it if you don't partition
> > the card. The next best thing is to align it to an RU which should be
> > pretty easy.
> >
> > You could guess the AU size by writting blocks of RU size from the start of
> > the card and timing it. Every time you hit the AU boundary there will be a
> > longer delay.
> >
> > For more details see the SD specification (chapter 4.13).
> >
> > https://www.sdcard.org/downloads/pls/
> >
> > They also have formatter tools for Windows and OSX. I tried the Windows
> > version years ago but had problems with it (can't remember what).
>
> Excellent information Fernando, thank you!
>
> So there is no tool for me to use to read the AU/RU on the chip?
>
> --
> Regards,
> Mick


Hi,

sorry for being a little late...was too busy and my sdcard is still
not formatted... ;)

Thank you very much for the help and all the informations. Currently I
start to understand the problems and solutions in formatting ONE
partition with a FAT32 filesystem on a sdcard the correct way, but 
when it comes to more the one partition and filesystems for example
like ext4fs I still dont know how to...

Just a few minutes before I found this:
http://www.bradfordembedded.com/2014/05/flashbenching/
http://wiki.laptop.org/go/How_to_Damage_a_FLASH_Storage_Device
https://github.com/bradfa/flashbench
http://wiki.laptop.org/go/SDCard_Testing
https://lists.linaro.org/pipermail/flashbench-results/
https://blogofterje.wordpress.com/2012/01/14/optimizing-fs-on-sd-card/

I am still in the process of reading and hopefully understanding
this...

Best regards,
Meino