On 2014-06-16 03:54, Swâmi Petaramesh wrote: > Hi, > > I created a BTRFS filesytem over LVM over LUKS encryption on an SSD [yes, I > know...], and I noticed that the FS got created with metadata in "DUP" mode, > contrary to what "man mkfs.btrfs" says for SSDs -> it would be supposed to be > "SINGLE"... > > Well I don't know if my system didn't identify the SSD because of the > LVM+LUKS > stack (however it mounts well by itself with the "ssd" flag and accepts the > "discard" option [yes, I know...]), or if the manpage is obsolete or if this > feature just doesn't work...? > > The SSD being a Micron RealSSD C400 > > For both SSD preservation and data integrity, would it be advisable to change > metadata to "SINGLE" using a rebalance, or if I'd better just leave things > the > way they are...? > > TIA for any insight. > What mkfs.btrfs looks at is /sys/block/<whatever-device>/queue/rotational, if that is 1 it knows that the device isn't a SSD. I believe that LVM passes through whatever the next lower layer's value is, but dmcrypt (and by extension LUKS) always force it to a 1 (possibly to prevent programs from using heuristics for enabling discard)
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