Thanks Mike, Great. I just look this picture and start to think pvmove must be what I want. http://www.redhat.com/magazine/007may05/features/storage/figs/pvmove.jpg - Akira On 2015/05/05 1:06, Mike Snitzer wrote: > On Mon, May 04 2015 at 6:37am -0400, > Akira Hayakawa <ruby.wktk@xxxxxxxxx> wrote: > >> Hi, >> >> Some DM target requires additional device that could be a single point of failure. >> Let's consider dm-cache. >> dm-cache requires a HDD and a SSD and if SSD is dead, the data is lost. >> To protect from this, SSD can be built RAID. But RAID isn't an ideal solution with SSD >> because the devices can be dead at the same time. Cost is the another problem of course. >> >> So, let's think about hotswap. >> A hotswap device has an active device and multiple ready devices. >> The active device is usually used and when the device is ordered to swap by >> a ready device it starts to sync the two devices and change the active device >> when sync is over. It's not simply dd-ing the devices because I/O isn't suspended and >> not all region is necessarily copied. >> You can order swapping whenever you like to. For example, swapping every week can be >> double the longevity of the cache device. >> >> I don't know how I can do this with DM targets. >> Do other part of linux technologies have such functinality? Please teach me if so. > > You could probably use lvm2's pvmove (it uses old dm-mirror target to swap over). > -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
