Interesting, this confirms what I was observing. Given the wording in man pages for "-m" and "-d" which states "Specify how the metadata or data must be spanned across the devices specified." I took "devices specified" to literally mean the devices specified after the according switch.
- DHC On Tue, Nov 19, 2013 at 3:06 AM, Hugo Mills <h...@carfax.org.uk> wrote: > 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. --- -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
