On Mon, Nov 18, 2013 at 11:12:03PM -0600, deadhorseconsulting wrote: > In theory (going by the man page and available documentation, not 100% > clear) does the following command indeed actually work as advertised > and specify how metadata should be placed and kept only on the > "devices" specified after the "-m" flag? > > Thus given the following example: > mkfs.btrfs -L foo -m raid10 <ssd> <ssd> <ssd> <ssd> -d raid10 <rust> > <rust> <rust> <rust> > > Would btrfs stripe/mirror and only keep metadata on the 4 specified SSD > devices? > Likewise then stripe/mirror and only keep data on the specified 4 spinning > rust?
No. The devices are general purpose. The -d and -m options only specify the type of redundancy, not the devices to use. There's a project[1] to look at this kind of more intelligent chunk allocator, but it's not been updated in a while. [1] https://btrfs.wiki.kernel.org/index.php/Project_ideas#Device_IO_Priorities > In trying and creating this type of setup it appears that data is also > being stored on the devices specified as "metadata devices". This is > observed through via a "btrfs filesystem show". after committing a > large amount of data to the filesystem The data devices have balanced > data as expected with plenty of free space but the SSD device are > reported as either nearly used or completely used. This will happen with RAID-10. The allocator will write stripes as wide as it can: in this case, the first stripes will run across all 8 devices, until the SSDs are full, and then will write across the remaining 4 devices. Hugo. -- === Hugo Mills: hugo@... carfax.org.uk | darksatanic.net | lug.org.uk === PGP key: 65E74AC0 from wwwkeys.eu.pgp.net or http://www.carfax.org.uk --- If it ain't broke, hit it again. ---
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