Size reported differently between profiles

Size reported differently between profiles

[Sébastien Luttringer]

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Hello,

«btrfs fi usage» report size differently between single,RAID0,RAID1,RAID5,RAID6
and RAID10.

The test is done with 2 files of 1.4GiB each on 4x10GiB devices. I used balance
to get size between profiles.

Data,single: Size:4.00GiB, Used:2.85GiB
   /dev/sdb	   1.00GiB
   /dev/sdc	   1.00GiB
   /dev/sdd	   1.00GiB
   /dev/sde	   1.00GiB

Data,RAID0: Size:8.00GiB, Used:2.85GiB
   /dev/sdb	   2.00GiB
   /dev/sdc	   2.00GiB
   /dev/sdd	   2.00GiB
   /dev/sde	   2.00GiB

Data,RAID1: Size:4.00GiB, Used:2.85GiB
   /dev/sdb	   2.00GiB
   /dev/sdc	   2.00GiB
   /dev/sdd	   2.00GiB
   /dev/sde	   2.00GiB

Data,RAID5: Size:6.00GiB, Used:2.85GiB
   /dev/sdb	   2.00GiB
   /dev/sdc	   2.00GiB
   /dev/sdd	   2.00GiB
   /dev/sde	   2.00GiB

Data,RAID6: Size:6.00GiB, Used:2.85GiB
   /dev/sdb	   3.00GiB
   /dev/sdc	   3.00GiB
   /dev/sdd	   3.00GiB
   /dev/sde	   3.00GiB

Data,RAID10: Size:4.00GiB, Used:2.85GiB
   /dev/sdb	   1.00GiB
   /dev/sdc	   1.00GiB
   /dev/sdd	   1.00GiB
   /dev/sde	   1.00GiB

For single,RAID0,RAID10 profiles, the sum of device sizes is equal to total size. Like total size is the "byte allocated size" for all devices.

For RAID1,RAID5,RAID6 profiles, sum of devices sizes is more than the total size. Looks like the redundancy was subtracted from the total.
Like total size is the "profile size allocated".

So, why RAID1 and RAID10 are reporting their sizes differently? This confuse me.

Cheers,

-- 
Sébastien "Seblu" Luttringer
https://seblu.net | Twitter: @seblu42
GPG: 0x2072D77A

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Re: Size reported differently between profiles

[Andrei Borzenkov]

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17.07.2016 05:09, Sébastien Luttringer пишет:
> Hello,
> 
> «btrfs fi usage» report size differently between single,RAID0,RAID1,RAID5,RAID6
> and RAID10.
> 
> The test is done with 2 files of 1.4GiB each on 4x10GiB devices. I used balance
> to get size between profiles.
> 
> Data,single: Size:4.00GiB, Used:2.85GiB
>    /dev/sdb	   1.00GiB
>    /dev/sdc	   1.00GiB
>    /dev/sdd	   1.00GiB
>    /dev/sde	   1.00GiB
> 
> Data,RAID0: Size:8.00GiB, Used:2.85GiB
>    /dev/sdb	   2.00GiB
>    /dev/sdc	   2.00GiB
>    /dev/sdd	   2.00GiB
>    /dev/sde	   2.00GiB
> 
> Data,RAID1: Size:4.00GiB, Used:2.85GiB
>    /dev/sdb	   2.00GiB
>    /dev/sdc	   2.00GiB
>    /dev/sdd	   2.00GiB
>    /dev/sde	   2.00GiB
> 
> Data,RAID5: Size:6.00GiB, Used:2.85GiB
>    /dev/sdb	   2.00GiB
>    /dev/sdc	   2.00GiB
>    /dev/sdd	   2.00GiB
>    /dev/sde	   2.00GiB
> 
> Data,RAID6: Size:6.00GiB, Used:2.85GiB
>    /dev/sdb	   3.00GiB
>    /dev/sdc	   3.00GiB
>    /dev/sdd	   3.00GiB
>    /dev/sde	   3.00GiB
> 
> Data,RAID10: Size:4.00GiB, Used:2.85GiB
>    /dev/sdb	   1.00GiB
>    /dev/sdc	   1.00GiB
>    /dev/sdd	   1.00GiB
>    /dev/sde	   1.00GiB
> 
> For single,RAID0,RAID10 profiles, the sum of device sizes is equal to
> total size. Like total size is the "byte allocated size" for all
> devices.
> 
> For RAID1,RAID5,RAID6 profiles, sum of devices sizes is more than the
> total size. Looks like the redundancy was subtracted from the total. 
> Like total size is the "profile size allocated".
> 
> So, why RAID1 and RAID10 are reporting their sizes differently? This
> confuse me.
> 

In your example only RAID10 is different. RAID1 shows 4GiB on 8GiB total
disks which matches "redundancy subtracted". But yes, I also wonder why
RAID10 does not respect it.


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