On 11/4/2018 11:44 AM, waxhead wrote:
Sterling Windmill wrote:
Out of curiosity, what led to you choosing RAID1 for data but RAID10
for metadata?
I've flip flipped between these two modes myself after finding out
that BTRFS RAID10 doesn't work how I would've expected.
Wondering what made you choose your configuration.
Thanks!
Sure,
The "RAID"1 profile for data was chosen to maximize disk space
utilization since I got a lot of mixed size devices.
The "RAID"10 profile for metadata was chosen simply because it *feels* a
bit faster for some of my (previous) workload which was reading a lot of
small files (which I guess was embedded in the metadata). While I never
remembered that I got any measurable performance increase the system
simply felt smoother (which is strange since "RAID"10 should hog more
disks at once).
I would love to try "RAID"10 for both data and metadata, but I have to
delete some files first (or add yet another drive).
Would you like to elaborate a bit more yourself about how BTRFS "RAID"10
does not work as you expected?
As far as I know BTRFS' version of "RAID"10 means it ensure 2 copies (1
replica) is striped over as many disks it can (as long as there is free
space).
So if I am not terribly mistaking a "RAID"10 with 20 devices will stripe
over (20/2) x 2 and if you run out of space on 10 of the devices it will
continue to stripe over (5/2) x 2. So your stripe width vary with the
available space essentially... I may be terribly wrong about this (until
someones corrects me that is...)
He's probably referring to the fact that instead of there being a
roughly 50% chance of it surviving the failure of at least 2 devices
like classical RAID10 is technically able to do, it's currently
functionally 100% certain it won't survive more than one device failing.
