On Wed, Jan 30, 2013 at 01:27:37AM -0800, Roger Binns wrote: > -----BEGIN PGP SIGNED MESSAGE----- > Hash: SHA1 > > I've been unable to find anything definitive about what happens if I use > RAID0 to join an SSD and HDD together with respect to performance > (latency, throughput). The future is obvious (hot data tracking, using > most appropriate device for the data, data migration). > > In my specific case I have a 250GB SSD and a 500GB HDD, and about 250GB of > files (constantly growing). One message I saw said that new blocks are > allocated on the device with the most free space which implies the SSD > would be virtually unused in my case, except for metadata which would only > be used half the time.
That would be the case with "single" mode, not with RAID-0. With RAID-0, you'd get data striped equally across all (in this case, both) the devices, up to the size of the second-largest one, at which point it'll stop allocating space. > At the moment I have two independent filesystems (one per device) and > manually move data files between them using symlinks to keep pathnames the > same. This requires keeping lots of slop free space on the SSD as well as > administration whenever it runs out of space. > > My hope would be overall performance between that of the two devices, and > closer to that of the SSD. We don't have any kind of hot-data management yet, but it's on the list of things we'd like to have at some point. Hugo. -- === Hugo Mills: hugo@... carfax.org.uk | darksatanic.net | lug.org.uk === PGP key: 515C238D from wwwkeys.eu.pgp.net or http://www.carfax.org.uk --- Some days, it's just not worth gnawing through the straps. ---
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