On Mon, Mar 27, 2017 at 01:17:26PM +0200, Christian Theune wrote: > Hi, > > I’m currently shrinking a device and it seems that the performance of shrink > is abysmal. I intended to shrink a ~22TiB filesystem down to 20TiB. This is > still using LVM underneath so that I can’t just remove a device from the > filesystem but have to use the resize command. > > Label: 'backy' uuid: 3d0b7511-4901-4554-96d4-e6f9627ea9a4 > Total devices 1 FS bytes used 18.21TiB > devid 1 size 20.00TiB used 20.71TiB path /dev/mapper/vgsys-backy > > This has been running since last Thursday, so roughly 3.5days now. The “used” > number in devid1 has moved about 1TiB in this time. The filesystem is seeing > regular usage (read and write) and when I’m suspending any application > traffic I see about 1GiB of movement every now and then. Maybe once every 30 > seconds or so. > > Does this sound fishy or normal to you?
On my hardware (consumer HDDs and SATA, RAID-1 over 6 devices), it takes about a minute to move 1 GiB of data. At that rate, it would take 1000 minutes (or about 16 hours) to move 1 TiB of data. However, there are cases where some items of data can take *much* longer to move. The biggest of these is when you have lots of snapshots. When that happens, some (but not all) of the metadata can take a very long time. In my case, with a couple of hundred snapshots, some metadata chunks take 4+ hours to move. Hugo. -- Hugo Mills | Great films about cricket: Silly Point Break hugo@... carfax.org.uk | http://carfax.org.uk/ | PGP: E2AB1DE4 |
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