On 2015-01-07 13:55, Kyle Gates wrote:
In theory, it would result in a greater degree of high-level fragmentation. You should (in theory) get marginally better performance by using no_ssd (or using a udev rule to set rotational to 1, as the flag is writable).What issues would arise if ssd mode is activated because of a block layer setting the rotational flag to zero? This happens for me running btrfs on bcache. Would it be beneficial to pass the no_ssd flag? Thanks, Kyle
Ideally, bcache shouldn't set the rotational flag to 0 unless the backing store (the big device that the cache is reading from) also has it set.
Also, ideally, we should be looking at the type of block device, not just whether the rotational flag is 0 or not, as there are a number of cases where rotational is 0 that enabling ssd will make things preform worse (Xen/Virtio block devices come immediately to mind).
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