Re: 6TB partition, Data only 2TB - aka When you haven't hit the "usual" problem

[Duncan <1i5t5.duncan@cox.net>]

Henk Slager posted on Mon, 11 Jan 2016 21:29:37 +0100 as excerpted:

> The Data increments with 1G (or 10G?) chunks if there is no well-fitting
> space in existing chunks.

One of the devs (Qu?) explained this rather well in a followup to 
something or other, probably about a week or two ago.  I remember 
replying to the effect of how much more I knew of the exact numbers at 
the time.

Based on that, nominal data chunk size is 1 GiB, on btrfs upto 100 GiB in 
size (tho real small ones will have smaller data chunk sizes as well, not 
sure of the small end numbers, tho when mixed-mode was introduced until 
progs 4.3(.1 I think), mixed-mode was the default below 1 GiB size, and 
it uses metadata sized chunks).  Above 100 GiB, data chunk size increases 
to 10 GiB.  Similarly, metadata chunk sizes are 256 MiB below 100 GiB, I 
think 1 GiB above.

As we're talking multi-TB in this case, obviously well above 100 GiB, 
data chunk sizes are likely to be 10 GiB, tho I'm not 100% sure if that 
applies on single device, or only to striped chunks, with 1 GiB strips 
and stripes of up to 10 GiB if there's 10 devices in the stripe.

(As regulars here will know if they've kept track, I use multiple, much 
smaller btrfs here, the largest of which is 24 GiB per device, pair-
device raid1 for both data/metadata, so 48 GiB total fs size, 24 GiB each 
on two devices in raid1, 24 GiB capacity.  Obviously I see only 1 GiB 
data chunks, smaller of course on my 256 MiB /boot and its backup on the 
other device, both of which are single-device mixed-mode dup, so 128 MiB 
capacity.)

-- 
Duncan - List replies preferred.   No HTML msgs.
"Every nonfree program has a lord, a master --
and if you use the program, he is your master."  Richard Stallman