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Ext4 filesystem hits Android, no need to fear data loss (ars technica)Ext4 filesystem hits Android, no need to fear data loss (ars technica)Posted Dec 28, 2010 8:33 UTC (Tue) by timokokk (subscriber, #52029)In reply to: Ext4 filesystem hits Android, no need to fear data loss (ars technica) by mikov Parent article: Ext4 filesystem hits Android, no need to fear data loss (ars technica)
"Doesn't Ext4 rely on a generic block layer? Isn't that going to significantly affect the reliability and life of the flash?"
Yes, ext4 relies on a generic block layer and it will not work on top of an mtd device. And no, it does not affect the reliability and life of the flash. If the device provides a generic block device interface, then it will also hide the raw flash layer and take care of the wear leveling for you. For example, eMMC memories work like that.
If you only have a raw flash device that does not hide the characteristics of the flash media, you will also need to use a file system that is designed to work with such media (JFFS2, UBIFS, whatever..).
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Ext4 filesystem hits Android, no need to fear data loss (ars technica) Posted Dec 28, 2010 12:39 UTC (Tue) by drag (subscriber, #31333) [Link]
Correct me if I am wrong, but It seems like most phones now with large amounts of on board storage use a SD-like device soldered to the mainboard.
So they often don't offer access to raw flash even if you wanted to use MTD directly.
Ext4 filesystem hits Android, no need to fear data loss (ars technica) Posted Dec 28, 2010 17:36 UTC (Tue) by mikov (subscriber, #33179) [Link]
May be so - it is probably much easier for the manufacturer. The question is how it affects reliability.
I doubt that the builtin SD controllers can perform very sophisticated wear leveling. It is an extremely difficult problem.
eMMC Posted Dec 28, 2010 14:37 UTC (Tue) by pflugstad (subscriber, #224) [Link]
I expect a lot of phones are using eMMC, due to it's lower pin counts compared to raw flash. eMMC presents a SCSI/block interface to the OS and so has it's own block translation and wear-leveling firmware which hides the underlying flash.
The problem with this is exactly that however - you're depending on the quality of the eMMC firmware, which can be dodgy. Look at the problems the SSD drives have had of falling off a performance cliff. Also, we've had issues with eMMC reliability from some vendors. I don't know if you can update that firmware on the fly or not.
We're to the point of putting bare NAND back on our boards and using UBIFS instead.
eMMC Posted Dec 28, 2010 18:14 UTC (Tue) by mikov (subscriber, #33179) [Link]
We are experiencing the same kind of problems, only unfortunately using bare NAND is not an option for us. That's why it seemed strange to me that large manufacturers like Samsung would voluntarily use the worse solution.
Ext4 filesystem hits Android, no need to fear data loss (ars technica) Posted Dec 28, 2010 20:42 UTC (Tue) by robert_s (subscriber, #42402) [Link]
"If you only have a raw flash device that does not hide the characteristics of the flash media, you will also need to use a file system that is designed to work with such media (JFFS2, UBIFS, whatever..)."
Not necessarily. You could always be using a software MTD-to-block translation/wear-levelling driver. I think a toy one is even shipped with the MTD layer.
Not sure how likely this solution is though.
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