F2FS experiences

[xyzzy]

Sorry, my bad, I should have written it more explicitly:
4KiB doesn't matter that much nowadays with regards to write amplification (read-modify-write cycles).

(i.e.: R-M-Ws will always happen upon in-place overwriting in a sub-part of an erase block).

Of course, it would matter to at least align the 4KiB block of an ext partitions with the 4KiB sectors, for read performance  (faster to read a single sector that to reads 2 sectors  and merge them).

(and given that the erase-block are a super-set of this sector layer, aligning to erase blocks to aleviate R-M-Ws will also get you aligned to sector boundary anyway).

But wouldn't a 4kB sector that is unaligned require writing two new blocks in an erase block, while an aligned sector would only require one?

It would be nice to be able to measure block erase count and total writes.  Then a benchmark could be done with aligned and unaligned fs blocks and the WAF measured.  It looks like JEDEC standard eMMC health has little detail and one would need a massive benchmark that used a significant portion of the total eMMC lifetime.  There is a Micron extension that could work.  Looks like PBP ships with a Sandisk eMMC.

Here is the command I used to measure random IO before and after aligning the partition with ext4.  It would be interesting to know how f2fs compares.

fio --randrepeat=1 --ioengine=libaio --direct=1 --gtod_reduce=1 --filename=test.fio --bs=4k --iodepth=64 --size=4G --readwrite=randrw --rwmixread=75 --name=aligned-ext4