On Sunday 15 November 2015 04:01:57 Duncan wrote: >audio muze posted on Sun, 15 Nov 2015 05:27:00 +0200 as excerpted: >> I've gone ahead and created a single drive Btrfs filesystem on a 3TB >> drive and started copying content from a raid5 array to the Btrfs >> volume. Initially copy speeds were very good sustained at ~145MB/s and >> I left it to run overnight. This morning I ran btrfs fi usage >> /mnt/btrfs and it reported around 700GB free. I selected another folder >> containing 204GB and started a copy operation, again from the raid5 >> array to the Btrfs volume. Copying is now materially slower and slowing >> further...it started at ~105MB/s and after 141GB has slowed to around >> 97MB/s. Is this to be expected with Btrfs of have I come across a bug >> of some sort? > >That looks to /me/ like native drive limitations. > [Snip nice explanation]
I'll just add that I see this with my 3TB USB3 HDD, too, but also with my internal HDDs. Old drives (the oldest I had were about 10 years old) also had this problem, only scaled appropriately (the worst was something like 40/60 GB/s min./max.). You can also see this very nicely with scrub runs (I use dstat for this): they start out at the max., but gradually slow down as they progress. HTH -- Marc Joliet -- "People who think they know everything really annoy those of us who know we don't" - Bjarne Stroustrup
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