btrfs raid5 with mixed disks

2015-02-09 Thread Rich Freeman 
How does btrfs raid5 handle mixed-size disks?  The docs weren't
terribly clear on this.

Suppose I have 4x3TB and 1x1TB disks.  Using conventional lvm+mdadm in
raid5 mode I'd expect to be able to fit about 10TB of space on those
(2TB striped across 4 disks plus 1TB striped across 5 disks after
partitioning).  How much would btrfs be able to store in the same
configuration?  I did see something about being able to use fixed-size
stripes, and I'm not sure if this helps.  If it does, are there any
penalties, especially with future expansion of the array?

With raid1 mode btrfrs is reasonably smart about mixed disk sizes, and
you usually end up with half of the total space available.

--
Rich
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Re: btrfs raid5 with mixed disks

2015-02-09 Thread Hugo Mills 
On Mon, Feb 09, 2015 at 05:24:42PM -0500, Rich Freeman wrote:
 How does btrfs raid5 handle mixed-size disks?  The docs weren't
 terribly clear on this.
 
 Suppose I have 4x3TB and 1x1TB disks.  Using conventional lvm+mdadm in
 raid5 mode I'd expect to be able to fit about 10TB of space on those
 (2TB striped across 4 disks plus 1TB striped across 5 disks after
 partitioning).  How much would btrfs be able to store in the same
 configuration?  I did see something about being able to use fixed-size
 stripes, and I'm not sure if this helps.  If it does, are there any
 penalties, especially with future expansion of the array?
 
 With raid1 mode btrfrs is reasonably smart about mixed disk sizes, and
 you usually end up with half of the total space available.

   http://carfax.org.uk/btrfs-usage/ may be useful here.

   Hugo.

-- 
Hugo Mills | It was half way to Rivendell when the drugs began
hugo@... carfax.org.uk | to take hold
http://carfax.org.uk/  |  Hunter S Tolkien
PGP: 65E74AC0  |Fear and Loathing in Barad Dûr


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