Can anyone explain why a log-structured file system is a good fit for flash? It seems that a lot of the benefits of an LFS are that it reduces disk seeks.
Samsung Creates New File System F2FS For Linux, Good News For Android
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Re: Samsung Creates New File System F2FS For Linux, Good News For Android
#12That's interesting, because every android device I've encountered (4-5 different models) have used YAFFS, which is also a NAND-friendly filesystem. Anybody know what the difference is?
As far as I know, YAFFS is not a journaled filesystem, and is really just a simple filesystem comparable in feature set to FAT32. F2FS looks like it's trying to bring the features of EXT3 to a flash-friendly implementation.
Re: Samsung Creates New File System F2FS For Linux, Good News For Android
#13Hopefully they'll do a better job than last time they tried this: the galaxy S had a custom filesystem called RFS, in reality it was just fat32 with crappy journaling bolted on. It totally crippled the phone, causing a lengthly block every time a file was closed. It would also fight with the chips own wear levelling algorithms. It sucked. If you owned that phone and thought it sucked, with loads of UI lag, it was bec…
I owned that phone, it did suck. The only good thing about that phone (besides the screen) is that it was nearly unbreakable and had a great custom Rom scene. Almost all of the roms replaced the file system.
And it still has a lot of custom rom support.
I'm writing from my Galaxy S with CM10 (Jellybean) now. Naturally, it uses Ext (3?) partitions, and resizes the cache partition so I can download apps larger than 30mb from the play store (another interesting file system choice from Samsung).
Re: Samsung Creates New File System F2FS For Linux, Good News For Android
#14File systems are extremely fickle things requiring the utmost attention to detail and quality. There is an impedance mismatch between that and most people's image of Samsung-produced software.
Yeah. Kies is slow as hell (more than iTunes on windows.. it says a lot, because iTunes on windows is not a shiny example of good software.) and TouchWiz is slowing down Android, sometimes destroying the battery and is otherwise a design sin, it's far more uglier than the stock UI, it's got better recently (S3, Note 10.1 etc.) but it still has some badly copied parts from iOS that doesn't really match Android's aesthetics, like the custom keyboard. The Samsung keyboard has an identical color scheme to iOS's virtual keyboards, it looks good on iOS because the rest of the interface is similar but it feels like total shit on Android and really it just proves that Samsung actually deserved to get bitchslapped in the courts by Apple because even an Android fan like myself could find too many similarities between what Samsung did to Android (it was worse for past devices) and iOS. Stock Android doesn't look like iOS, but TouchzWiz used to, and some parts of TouchWiz still do to this day (like the keyboard I mentioned).
I love Android, and I like some of Samsung's hardware but I wish they'd shut their whole software division down and just put stock android on their phones and tablets. Stop writing code, and stop designing your custom UI, because you SUCK at this job.
Re: Samsung Creates New File System F2FS For Linux, Good News For Android
#15Can anyone explain why a log-structured file system is a good fit for flash? It seems that a lot of the benefits of an LFS are that it reduces disk seeks.
You want writes to flash to be as sequential as possible. Random writes to flash result in more wear and worse performance due to GC overhead.
Log-structured file systems tend to write data sequentially since the writes append to the log (yes - that's a gross over simplification).
File systems like ext4 maintain separate data structures for data and metadata and generate more random writes.
Re: Samsung Creates New File System F2FS For Linux, Good News For Android
#16Can anyone explain why a log-structured file system is a good fit for flash? It seems that a lot of the benefits of an LFS are that it reduces disk seeks.
That article is pretty light on the details, but one thing to note is that most sd card storage is relatively poor at random seeks, having been optimized for media type usage.
Re: Samsung Creates New File System F2FS For Linux, Good News For Android
#17Can anyone explain why a log-structured file system is a good fit for flash? It seems that a lot of the benefits of an LFS are that it reduces disk seeks.
It has to do with the way flash does writes. In flash it actually takes longer to overwrite a bit of data, than to write that bit on a 'blank', or previously initialized cell.
Furthermore if you are going to overwrite something in flash it usually behooves you to overwrite an entire block at a time. For these reasons flash systems tend to try to often write changes in a log manner, wait for a lot of changes to pile up and then incorporate those changes back into the original by rewriting entire blocks. The log can be placed in an initialized section of the memory where overwrites are not necessary.
Re: Samsung Creates New File System F2FS For Linux, Good News For Android
#18That's interesting, because every android device I've encountered (4-5 different models) have used YAFFS, which is also a NAND-friendly filesystem. Anybody know what the difference is?
As far as I know, YAFFS is not a journaled filesystem, and is really just a simple filesystem comparable in feature set to FAT32. F2FS looks like it's trying to bring the features of EXT3 to a flash-friendly implementation.
YAFFS is a log-structured filesystem, just like F2FS. Log-structuring gives you a data organization protocol. This protocol gives you an implicit crash-recovery story, there is no need for additional journaling on top of it.
Journalling is used when some blocks on the disk are scheduled to be overwritten. Instead, the blocks are written in a separate location (the so-called journal). At a later point in time, the data blocks get overwritten. Once the data is safely on the disk (via Forced Unit Access (FUA) or a flush track cache-type operation) we can then truncate the journal.
Log-structured systems do not do this. Instead, the achieve crash safety via never overwriting data; they always write elsewhere (into something called 'the log'). Eventually, too much of this log is filled with garbage, stale data. This is when 'cleaning' occurs. However, cleaning is expensive and slow. You must read a large amount of data, figure out what is alive/dead, and then write it all out.
F2FS's contribution to FS design seems to be handling this cleaning operation in a more graceful manner.
Re: Samsung Creates New File System F2FS For Linux, Good News For Android
#19Earlier quoted context omitted.
As far as I know, YAFFS is not a journaled filesystem, and is really just a simple filesystem comparable in feature set to FAT32. F2FS looks like it's trying to bring the features of EXT3 to a flash-friendly implementation.
YAFFS is a log-structured filesystem, just like F2FS. Log-structuring gives you a data organization protocol. This protocol gives you an implicit crash-recovery story, there is no need for additional journaling on top of it. Journalling is used when some blocks on the disk are scheduled to be overwritten. Instead, the blocks are written in a separate location (the so-called journal). At a later point in time, the dat…
Thanks, that's an awesome summary, and good to know. :)
Re: Samsung Creates New File System F2FS For Linux, Good News For Android
#20Can anyone explain why a log-structured file system is a good fit for flash? It seems that a lot of the benefits of an LFS are that it reduces disk seeks.
It has to do with the way flash does writes. In flash it actually takes longer to overwrite a bit of data, than to write that bit on a 'blank', or previously initialized cell. Furthermore if you are going to overwrite something in flash it usually behooves you to overwrite an entire block at a time. For these reasons flash systems tend to try to often write changes in a log manner, wait for a lot of changes to pile u…
> Furthermore if you are going to overwrite something in flash it usually behooves you to overwrite an entire block at a time.
Well, all block devices are written a block at a time. The way flash differs is that there are two internal block sizes -- called pages (4-8kB), and eraseblocks (256kB-4MB).
There are two states a page can be in: clear, or used. You can write at a page granularity, but only to clear pages. To clear used pages, you need to clear the entire eraseblock at a time. Eraseblock sizes are now limited by fundamental physical limits -- on every NAND node shrink from now, the eraseblocks are going to double in size. And they are already really huge in modern devices.