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Old 09-13-2010, 04:08 AM   #1
AleLinuxBSD
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What about SDXC Memory Cards?


Yes i read about Tuxera and their solution for embedded system even on linux but don't exist some project free?

SDHC and SDXC compatibility issues
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SDHC and SDXC compatibility issues

In the 3.0 specification, the electronic interface of SDHC and SDXC cards is the same. The decision to label cards with a capacity greater than 32GB as SDXC and to use a different filesystem is due solely to the limitations in creating larger filesystems in certain versions of Microsoft Windows. Other operating systems, such as Linux, make no distinction between SDHC and SDXC cards, as long as the card contains a compatible filesystem.

SDHC and SDXC cards and devices have these compatibility issues:

* SDHC devices will only support the SDXC cards which use UHS104 speeds;[31] SDHC devices will not recognize the SDXC cards which use the faster (SD 4.0), final specification of SDXC.[46]
* SDXC devices are backward compatible with SD and SDHC memory cards.[46]
* Linux (with a proprietary driver for the exFAT filesystem[47]), Microsoft Windows 7/Vista SP1+[46]/XP SP2+ (with exFAT update),[48] and Mac OS X Snow Leopard (on the Mac Mini released in June 2010 & iMac released in July 2010)[49] are the only operating systems to currently support SDXC.
So essentially is possible use this memory card as mass storage but if you want use it for manage data taken using photo camera or video camera (that use exFat, the propetary file system of microsoft), don't exist any open solution for linux?
 
Old 09-14-2010, 08:56 AM   #2
Skaperen
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The technical specifications for SDHC would physically support up to 2TB capacity. However, the standard states the limit as 32GB. It is unknown whether this discrepancy is due to their own miscalculations, or some ulterior motive. It may well be that Microsoft has pressured them into drawing the line at 32GB due to lack of filesystem support as your references describe.

I don't use FAT filesystems on my SD{,HC,XC} cards (or USB memory sticks). I do a variety of other things, from using an ext2 filesystem, an ISO-9660 filesystem (I have a toolkit that makes ISO images bootable on these devices while also keeping it bootable on CD/DVD via El-Torito), or writing cpio or tar output onto raw sectors (usually partitioned). I usually do not need to be Windows compatible, so I use whatever works better for me. In the rare instances I do need to be Windows compatible, I have retained a compressed copy of the original card contents (the "xz" compression tool usually makes the tightest compression) which I can restore if I need to make it Windows compatible, again. When things get above 32GB, or more specifically when I need to make more than 32GB be Windows compatible, then I guess I will have to use this exFAT or else something like NTFS.

I have heard newer cameras (the market where SD{,HC,XC} cards are aimed at) are supporting SDXC, now. I suppose an SDXC 64GB card would have this exFAT already formatted on it, so that would be a starting point to test things with Linux. Of course, I could always just re-partition with 32GB or smaller partitions, format with FAT32, and split up the files.

I wonder if Windows would recognize an ISO filesystem on one of these cards or a USB memory stick.

As for open source solutions to exFAT, no doubt someone will reverse engineer exFAT and make at least an application level tool that can extract files from exFAT (much like mtools did for floppies). And someone may also make a kernel module.

You might also check out this project, a FUSE based exFAT: http://code.google.com/p/exfat/

Last edited by Skaperen; 09-14-2010 at 09:08 AM. Reason: ref fuse based exfat
 
Old 09-14-2010, 10:38 AM   #3
AleLinuxBSD
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Good to hear that at least is already started the FUSE based project.
Now this memory are expensive and the old dispositive can't use it, so for the moment isn't a problem, but i hope that when the cost of this memory decrease and there will more widespread the alternative free solution linux will be ready.
(Even only a stable read only solution is sufficient).
After that could came even the write thing as happen on the past for other problematic file system (as for example Ntfs).
I hope also the exFAT is more easy respect NTFS for implement it on short time without problem.
 
Old 09-14-2010, 01:28 PM   #4
Skaperen
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I agree that a read-only need would be priority for Linux. Linux needs to be able to read pictures stored by cameras. Uses where Linux needs to write and Windows needs to read would be the alternate case where a writing solution is needed. But I suspect lesser need for this (because there are alternatives for most cases, such as splitting a large card into partitions, or using multiple smaller cards, or just using a network if the computers are close enough).

I'm curious what filesystem comes on the 2TB "spinning metal platter" USB drives for comparison. Why can't we do the same which was on a 128GB metal drive for any 128GB flash drive (SDXC memory card or USB memory stick)? I do have a 1.5TB USB drive. I did save the original contents (took a day to read it all sequentially while compressing with gzip ... and over a week to uncompress with gunzip while recompressing with xz) before wiping it and formatting it for Linux with ext3, so maybe I can peek into that sometime and see.
 
  


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