Chris Murphy posted on Tue, 02 Sep 2014 20:44:06 -0600 as excerpted: > On Sep 2, 2014, at 12:40 AM, Duncan <1i5t5.duncan@xxxxxxx> wrote: >> >> Mkfs.btrfs used to default to 4 KiB node/leaf sizes; now days it >> defaults to 16 KiB as that's far better for most usage. I wonder if >> USB sticks are an exception… > > USB sticks > 1 GB get 16KB nodesize also. Seems you read into that a meaning I didn't even consider when I wrote it. =:^/ I /meant/ that AFAIK mkfs.btrfs did the usual 16K thing, but that perhaps (some, depending on erase-block size) USB sticks are an exception to 16K being better than 4K thing. > At <= 1 GB, mixed-bg is > default as is 4KB nodesize. Probably because queue/rotational is 1 for > USB sticks, they mount without ssd or ssd_spread which may be > unfortunate (I haven't benchmarked it but I suspect ssd_spread would > work well for USB sticks). I did mention ssd_spread somewhere in my replies, due to the same suspicion. Good to see you have the same suspicion I do. =:^) > It was suggested a while ago that maybe mixed-bg should apply to larger > volumes, maybe up to 8GB or 16GB? Indeed. Considering the default data chunk size is 1 GiB, that as the cutoff for default mixed-bg mode seems kinda low. If anything, I think 16 GiB is still a low cutoff value, at least as long as the only way to reclaim out-of-balance data/metadata assigned chunks is via a manual balance. I'd suggest a 32 GiB cutover by default. Tho if btrfs gets a good auto-balance-trigger mechanism that say triggers when allocated (fi show device figure) is within say 10% of total filesystem space (rounded up to the nearest GiB, minimum 2 GiB) AND data or metadata has more than say 10% spread between used and allocated (fi df, again rounded up, 2 GiB minimum), that can arguably come down a notch, to say 16 GiB. -- Duncan - List replies preferred. No HTML msgs. "Every nonfree program has a lord, a master -- and if you use the program, he is your master." Richard Stallman -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
