[Galaxy S I9000 Android Development] justcme:
I too, have noticed that battery seems to be draining faster than before - but only when using the phone.

Idle drain has been excellent, much like before. This morning, had my SGS on idle for about 4 hours (wifi off, mobile data on, gmail sync on, 15min twitter sync on launcherpro widget), and it only dropped 5-6%.

However, as soon as I started using the phone after that the battery started dropping rapidly. What do I mean by using? Just turning the screen on, basically; and a bit of browsing.

But why would this be the case? I don't know, considering that any number of things could be happening. It could be purely subjective - all of us are hallucinating and wanting more battery life after living with a speedier UI. After all, we all know that the SGS's display is the biggest battery killer of them all; so maybe it's just that. That said, apart from the very real performance results of using ext4 on /data, we still don't really know its effect on CPU load and battery life. Assuming the kernel curio has provided us (with ext4 support) is essentially the stock kernel, there might be reason to suspect any additional battery drain during use could be due to ext4. Or maybe not!

Sure, we might not really be writing much to /data much (unless we try new apps all the time, or keep changing the widgets in launcherpro - I noticed heavy launcherpro lag when adding and removing widgets under RFS), but surely under a journalled filesystem, the act of reading data from the FS would incur a heavier CPU load due to integrity checks on the data? Well, I don't know for sure, just a guess. Journalling writes obviously impose a greater CPU load and more SD card writes, but I don't know about reads. And how ext4 compres to RFS in this regard? There hasn't been any information from anyone (here or elsewhere) yet. There are lots of filesystems with benchmarks for linux (ext2, ext3, ext4, btrfs, reiserfs, reiser4, xfs, jfs to name a few) available on the net in various places, discussing performance and reliablity etc, and one or two have some information about CPU loading and the effects on flash as well. How this translates to our phones is probably another matter though, but it's useful to have a bit more knowledge in this area.

Back in the days of 1-2hrs laptop battery times, I remember reading about JFS being lightest on CPU load while achieving decent performance, and XFS being great with lots of small files, and reiserfs being a huge bottleneck when writing lots of small files, etc. Having a mechanical HDD was a real batttery drain too, so picking the right journaled FS mattered back then IMO.

EDIT: I guess my point is picking an FS is more than just about performance, and like anything else, there's lots of variables to consider. But given we are on 1GHz mobile phones with 1500mAh batteries and advanced flash memory, I'm not sure how much it matters. It's not like we're running a database server or working with large video files. Perhaps logcat is writing to a file on the RFS/ext4 partition somewhere? D: Anyhow, take my rambling as a grain of salt, if possible. :)

So all this is just something to think about. Maybe it has no effect at all.

For those observing additional battery drain - myself included - try and take note of when in particular it's draining fastest. I know my idle SGS drains very little, but using certain apps (browser, news apps) has been killing the battery much faster than before. (Gaming appears to have no additional adverse effects on battery - apart from eating it up like it usually does).

As an aside, supercurio, what's the performance like for voodoo under ext2? I'm not sure what useful data is actually stored in /data (apart from apps and app configuration), but for me personally, most of my important data is stored in the cloud anyway (contacts, emails), and our sms/mms live in /dbdata. And other things live on our FAT32 partitions of our internal & external SD cards - not really any much safer than using ext2 IMHO. What problems were you foreseeing with data corruption under ext2? I'd love to test an ext2 version, if you could provide one. :D Just for educational purposes! :P Apologies if you have already reported information about ext2 that I missed. Please correct me anywhere I've just gone off completely and said the wrong thing, by the way. :)

Anyhow, maybe all of this is just placebo. The bad kind. D:

Just my 2(00)cents. :)

EDIT: An old (2004), but nevertheless interesting article about RFS and Samsung's claims.

http://www.linuxfordevices.com/c/a/News/Samsung-aims-new-NAND-Flash-filesystem-at-Linuxbased-gadgets/

EDIT: RFS is just FAT16 (maybe 32?) with transaction logging. http://movitool.ntd.homelinux.org/trac/movitool/wiki/RFS.

EDIT: Links are provided for those who don't know already know these things, of course. :)