Btrfs devel - Jan 2012 - btrfs on ssd and hdd

Hi,
I am using for my workspace btrfs filesystem on ssd disk. I do not thrust to my
ssd and I want to have backup of all data on rotational hdd (raid5 of 5 disks).
If I am not wrong, this can be done when I use btrfs on top of two phycical
media (one ssd and second md device). This I think would work fine.

My question is, does btrfs recognize poor latency of md device and will preform
most reads from ssd? (I want to set raid1 for metadata and also to data). (side
question, should be ssd in parameters of mount?)

PS: Is this crazy idea, or normal (planned) usecase?

Thanks for clarification,
LuVar
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On Sat, 14 Jan 2012 16:02:23 +0100 (GMT+01:00)
luvar@plaintext.sk wrote:
> I am using for my workspace btrfs filesystem on ssd disk. I do not thrust
to my ssd and I want to have backup of all data on rotational hdd (raid5 of 5
disks). If I am not wrong, this can be done when I use btrfs on top of two
phycical media (one ssd and second md device). This I think would work fine.
> 
> My question is, does btrfs recognize poor latency of md device and will
preform most reads from ssd? (I want to set raid1 for metadata and also to
data). (side question, should be ssd in parameters of mount?)
> 
> PS: Is this crazy idea, or normal (planned) usecase?
Hello,

This is not a crazy idea, and it''s already possible in MD-based RAID.
Run ''man md'' and ''man mdadm'' and do a search
for ''write-mostly'' to read more about it.

However I don''t think the same feature has been implemented in BTRFS
yet.

-- 
With respect,
Roman

~~~~~~~~~~~~~~~~~~~~~~~~~~~
"Stallman had a printer,
with code he could not see.
So he began to tinker,
and set the software free."