For having a *guaranteedly intact* storage, what is the way then? This is with the background of recent discussions that touched on https://www.usenix.org/legacy/events/fast08/tech/full_papers/bairavasundaram/bairavasundaram_html/index.html and https://blog.algolia.com/when-solid-state-drives-are-not-that-solid/ .
What about having *two SSD*:s in softraid RAID1, and as soon as any IO failure is found on either SSD, that one would be replaced? If the underlying read operations are made from both SSD:s each time and the machine has ECC RAM (??and UFS is checksummed enough??), then at least the OS would be able to detect corruption (??, fix anything??) and return proper read failures (or sigsegv) properly. Mikael 2015-06-18 16:23 GMT+07:00 Karel Gardas <gard...@gmail.com>: > 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
