Re: btrfs RAID-1 vs md RAID-1?

[Kai Krakow <hurikhan77@gmail.com>]

Am Sun, 15 May 2016 19:24:47 +0900
schrieb Tomasz Chmielewski <mangoo@wpkg.org>:

> I'm trying to read two large files in parallel from a 2-disk RAID-1 
> btrfs setup (using kernel 4.5.3).
> 
> According to iostat, one of the disks is 100% saturated, while the
> other disk is around 0% busy.
> 
> Is it expected?
> 
> With two readers from the same disk, each file is being read with ~50 
> MB/s from disk (with just one reader from disk, the speed goes up to 
> around ~150 MB/s).
> 
> 
> In md RAID, with many readers, it will try to distribute the reads - 
> after md manual on http://linux.die.net/man/4/md:
> 
>      Raid1
>      (...)
>      Data is read from any one device. The driver attempts to
> distribute read requests across all devices
>      to maximise performance.
> 
>      Raid5
>      (...)
>      This also allows more parallelism when reading, as read requests
> are distributed over all the devices
>      in the array instead of all but one.
> 
> 
> Are there any plans to improve this is btrfs?
> 
> 
> Tomasz Chmielewski
> http://wpkg.org

Here is an idea that could need improvement:
http://permalink.gmane.org/gmane.comp.file-systems.btrfs/17985


-- 
Regards,
Kai

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