On Thu, Jun 18, 2015 at 9:08 AM, David Dahlberg <david.dahlb...@fkie.fraunhofer.de> wrote: > Am Donnerstag, den 18.06.2015, 02:15 +0530 schrieb Mikael: > >> 2015-06-18 2:07 GMT+05:30 Gareth Nelson <gar...@garethnelson.com>: >> No I meant, you plug in a 2TB SSD and a 2TB magnet HD, is there any way to >> make them properly mirror each other [so the SSD performance is delivered >> while the magnet disk safeguards contents] - would you use softraid here? > > No. If you use a RAID1, you'll get the performance of the worse of both > disks. To support multiple disks with different characteristics and to > get the most out of it was AFAIK one of motivations for Matthew Dillon > to write HAMMER. >
I'm not sure about RAID1 in general, but I'm reading softraid code recently and based on it I would claim that you get write performance of the slowest drive (assuming OpenBSD schedule writes to different drives in parallel), but read performance slightly higher than slower drive since the read is done in round-robin fashion hence SSD will speed it a little bit. Anyway, the interesting question is if it makes sense to balance this interleaving reading based on actual drive performance. AFAIK this should be possible, but IMHO it'll not be that reliable, i.e. it'll not provide that much of added reliability. Since reliability is my concern, I'm more looking forward to see kind of virtual drive with implemented block checksumming in OpenBSD, that IMHO will provide some added reliability when run for example in RAID1 setup. Karel
