On 13 February 2016 at 08:50, Tinker <ti...@openmailbox.org> wrote: > Hi, > > 1) > http://www.openbsd.org/papers/asiabsdcon2010_softraid/softraid.pdf page 3 > "2.2 RAID 1" says that it reads "on a round-robin basis from all active > chunks", i.e. read operations are spread evenly across disks.
Yes, that's still the case today: http://bxr.su/o/sys/dev/softraid_raid1.c#sr_raid1_rw 345 rt = 0; 346ragain: 347 /* interleave reads */ 348 chunk = sd->mds.mdd_raid1.sr1_counter++ % 349 sd->sd_meta->ssdi.ssd_chunk_no; 350 scp = sd->sd_vol.sv_chunks[chunk]; 351 switch (scp->src_meta.scm_status) { 356 case BIOC_SDOFFLINE: 359 if (rt++ < sd->sd_meta->ssdi.ssd_chunk_no) 360 goto ragain; There are presently no optimisations in-tree, but the softraid policies are so simple that it's really easy to hack it up to do something else that you may want. > > Since then did anyone implement selective reading based on experienced read > operation time, or a user-specified device read priority order? That would make the code less readable! :-) > > > That would allow Softraid RAID1 based on 1 SSD mirror + 1 SSD mirror + 1 HDD > mirror, which would give the best combination of IO performance and data > security OpenBSD would offer today. Not sure what'd be the practical point of such a setup. Your writes will still be limited by the slowest component, and IOPS specs are vastly different between SSDs and HDDs. (And modern SSDs are no longer considered nearly as unreliable as they once were.) > > 2) > Also if there's a read/write failure (or excessive time consumption for a > single operation, say 15 seconds), will Softraid RAID1 learn to take the > broken disk out of use? A failure in a softraid1 chunk will result in the chunk being taken offline. (What constitutes a failure is most likely outside of softraid's control.) C.
