I'm just curious if anyone has ever tried an installation that has no BSAs and no compression of any kind, and if so, what sorts of performance benefits you saw.
I'm thinking about unzipping absolutely everything into the Data folder (and updating the Oblivion.ini file to match). Thoughts are appreciated.

I asked the same question long time ago, and some people said that the performance of uncompressed BSA is equal to that of loose files.
Since it is easier to manage BSA, loose files are not quite recommended.
You can unpack the original BSA files from Bethesda and repackage them with uncompressed setting. They are in compression by default, so repackaging them without compression should improve some performance.

Actually doing this would be far worse than uncompressed BSAs because all these loose files (thousands of them) would fragment all over the drive. Even if the drive were defragged, you'll still get a better boost out of the uncompressed files because those would defrag all as one chunk vs 50,000+ tiny little ones.

I had to unpack the John's Leveled List Overhaul BSA to get it working ( weird, weird Oblivion ) , as long as you don't have TOO MUCH stuff unpacked you should be fine... a fast HDD or an SDD would be nice though.

take a look at http://obge.paradice-insight.us/wiki/NIFopt#A_little_calculation

Reading compressed data is faster than reading uncompressed data? Seriously?
If so, I will just put all loose files from other mods together and compress them into BSAs.

Well, then you have the problem of making the BSAs load in the proper order. Since loose files overwrite BSA files, putting replacers in BSAs is not always a good idea. If your content is all new, then a BSA would work fine.

Please, someone more knowledgeable correct me if I am wrong, but I seem to remember threads that demonstrate more problems after trying to compress everything into BSAs. Plus, I've never seen conclusive evidence of noticeable performance increase.

Heh, this is turning out to be a better discussion than I anticipated!

You can't put replacers in BSAs. Oblivion's BSA handling will, at best, randomize what you get back from that, and at worst, crash the game due to the conflict. If you're replacing vanilla content, it HAS to be loose files. BSAs are only suitable for new content.

Well, I don't manage to create new BSA, but I will use the original BSA instead.
I mean, I will unpack the original BSAs and put new meshes/textures to overwrite vanilla ones, and repackage them with compression. Since compressed BSAs have benefit in speed theoretically, I think it is worth putting mesh/texture replacement mods(QTP3, for example) into original BSAs.

Ah. Yes, that's more or less what I did, only all the files I generated are uncompressed.

So you're using uncompressed BSA's? What would be the benefit of that?

game is quicker to read them i.e. load them.

Hmmm...
According to http://obge.paradice-insight.us/wiki/NIFopt#A_little_calculation, game could be slower when using uncompressed BSAs because the uncompressed file size is so big that game takes more time to read than decompress.
It's interesting that uncompressed BSAs may not take as much benefit as we expect.

What's best will depend on your specific hardware. A slow harddrive will probably see more benefit from compression than a zippy SSD will.
SSDs will also handle loose files much better due to their faster seek time, I've been thinking of running a setup with extracted BSAs when I get an SSD.

I have a 120GB SSD for system drive, but I intend not to install games on it because constant writing will shorten SSD's lifetime, not to mention that Oblivion need to install and uninstall many mods frequently.

It had a large enough effect for me that running uncompressed was a noticable improvement to stutter, if not actual CPU attention. Decompression isn't a zero cost operation. With as many mods as I run, devoting time to decompression hurts.

Plus, having a nice, easy to uninstall file keeps things quite organized no doubt.

I tried a large overhaul that did not have a bsa and load times were incredibly terrible! No stutter though.

True, for large mods it is often better to consolidate into a BSA. Due to file limits though I'd reserve that for the truly large ones with at least several hundred files, if not into the low thousands.

If you disable hard drive caching, that'll eliminate a lot of the writing. In theory, it should pretty much limit the writing to game saving.

Side note: having a 120 GB SSD and not using it for games to make it last longer is kind of missing the point.

With a typical 3-year-old SATA drive, I gained a huge performance boost after I bsa'd-without-compression every mod I have installed that was not a replacer. I also merged all the UOP resources (since I will never not want those, ever) into the stock bsa files, and re-packed those without compression. Huge gain, and worth it in every way.

If a bsa file is so large that it would be faster read with compression, then just split the bsa file into two and re-pack each uncompressed for even greater gain.

Much like merging .esp files, you can also merge .bsa files when you repack them. If you have two dozen mods that you always keep around, such as all the UL mods for example, or your favorite dozen outfits, you can always pack their resources into a single bsa. This can help avoid the file limit without having many loose files.

I can definitely testify to this...on my initial install I made the mistake of compressing every single voice file from Oblivion - Voices1, Oblivion - Voices2, and all of the unofficial patches into the same file. They barely fit under the 2GB limit, even with maximum forced compression. Needless to say the in-game performance was pretty bad.