Am Samstag, 27. Dezember 2014, 06:00:48 schrieb Robert White: > On 12/27/2014 05:16 AM, Martin Steigerwald wrote: > > It can easily be reproduced without even using Virtualbox, just by a nice > > simple fio job. > > TL;DR: If you want a worst-case example of consuming a BTRFS filesystem > with one single file... > > #!/bin/bash > # not tested, so correct any syntax errors > typeset -i counter > for ((counter=250;counter>0;counter--)); do > dd if=/dev/urandom of=/some/file bs=4k count=$counter > done > exit > > > Each pass over /some/file is 4k shorter than the previous one, but none > of the extents can be deallocated. File will be 1MiB in size and usage > will be something like 125.5MiB (if I've done the math correctly). > larger values of counter will result in exponentially larger amounts of > waste.
Robert, I experienced this hang issues even before the defragmenting case. It happened while just installed a 400 MiB tax returns application to it (that is no joke, it is that big). It happens while just using the VM. Yes, I recommend not to use BTRFS for any VM image or any larger database on rotating storage for exactly that COW semantics. But on SSD? Its busy looping a CPU core and while the flash is basically idling. I refuse to believe that this is by design. I do think there is a *bug*. Either acknowledge it and try to fix it, or say its by design *without even looking at it closely enough to be sure that it is not a bug* and limit your own possibilities by it. I´d rather see it treated as a bug for now. Come on, 254 IOPS on a filesystem with still 17 GiB of free space while randomly writing to a 4 GiB file. People do these kind of things. Ditch that defrag Windows XP VM case, I had performance issue even before by just installing things to it. Databases, VMs, emulators. And heck even while just *creating* the file with fio as I shown. Ciao, -- Martin 'Helios' Steigerwald - http://www.Lichtvoll.de GPG: 03B0 0D6C 0040 0710 4AFA B82F 991B EAAC A599 84C7 -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
