On 2018-09-19 04:43 AM, Tomasz Chmielewski wrote: > I have a mysql slave which writes to a RAID-1 btrfs filesystem (with > 4.17.14 kernel) on 3 x ~1.9 TB SSD disks; filesystem is around 40% full. > > The slave receives around 0.5-1 MB/s of data from the master over the > network, which is then saved to MySQL's relay log and executed. In ideal > conditions (i.e. no filesystem overhead) we should expect some 1-3 MB/s > of data written to disk. > > MySQL directory and files in it are chattr +C (since the directory was > created, so all files are really +C); there are no snapshots. Not related to the issue you are reporting, but I thought it's worth mentioning, (since not many do), that using chattr +C on a BTRFS Raid 1 is a dangerous thing. without COW, the 2 copies are never synchronized, even if a scrub is executed. So any kind of unclean shutdown that interrupts writes (not to mention the extreme of a temporarily disconnected drive.) will result in files that are inconsistent. (ie, depending on which disk happens to read at the time, the data will be different on each read.)
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