ReadyNas 6.2 (NAS locks up entirely)

jaffacake wrote:
Define "a lot of snapshots"? Taking hourly snapshots is always going to add up to a lot of them...24 each day per share. As I understand it, btrfs is very efficient with snapshots so this shouldn't be a major issue.

The impact of snapshots on file system performance is complex, so I don't think it lends itself to a crisp definition.

Also, "efficient" has more than one dimension. BTRFS snapshots are very space efficient. Make a new snapshot is computationally efficient.

Maintaining snapshots as files are changed is another matter. It can take some time, and it results in file fragmentation. There is a web of reflinks between each snapshot folder (+ the main folder) and the file data on the disk, and every time you change a file those reflinks need to be adjusted (and over time the number of reflinks grows). Maintaining snapshots is space efficient, but performance will drop. How much it drops depends on the usage pattern.

One scenario - you have a media library. You regularly add files, but don't change them, and deletions happen rarely. In this case, snapshots gradually pick up the deleted files. There isn't any fragmentation, because the files aren't being modified. Read and write performance will be good, and shouldn't change much as the number of snapshots grows.

Another scenario - you have a torrent folder. New torrents are being added all the time, and more importantly new torrent pieces are being received every second. You make a snapshot on the hour, right after a torrent starts. A second later, 3 torrent pieces have arrived. The file system has to maintain the original unwritten disk blocks in the snapshot, and link in new disk blocks in the main share for the newly arrived pieces. That takes some work, and the file ends up fragmented. This process continues, and you end up with a completely fragmented file by the time the torrent completes. Read performance and write performance will suffer. Total space usage for each file will end up at least 2x its size, and likely will be more than that if multiple snapshots are taken while the torrent is running (It also depends on the torrent piece size, and how the pieces are aligned with the file system data blocks. Each data block is written at least once after the file is created and initial space allocated, but some data blocks are written more than once because they hold multiple pieces that arrive at different times).

The net here is that snapshots aren't a one-size-fits-all kind of feature. You do need to set up the share options with the expected usage patterns in mind. If you don't do that, then throughput will suffer.