Re: Using Btrfs on single drives

[Marc Joliet <marcec@gmx.de>]

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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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