On Sat, Jan 31, 2004 at 03:36:21PM -0600, Nathan Lewis wrote: > Even if it were possible, your write performance would be TERRIBLE (imaging > writing the chunks in order - 0, 1, 2, 3.... Your disk heads would be > thrashing constantly). Well, I am not sure that will be so. Most modern disks today have buffers of 2 MB - 8 MB on the unit, and writes would thus be buffered there, meaning that the drive would be striping. > The RAID1 code already does read-balancing. Not > the same thing as striping, but certainly increases performance on reads, > especially when more than one read is being done at a time. Yes, striping is best when there is only one read or write in operation. I think tho, that lonely sequential reads or writes are very common, even on servers. > > If you wanted to try it, I think you might be able to accomplish it with > partitions. Partition your two disks in half, so you have: > disk1 a & b > disk2 a & b > > Then mirror disk1a with disk2b (say as /dev/md0), and likewise mirror > disk1b with disk2a (say as /dev/md1). Then create a RAID0 array (/dev/md2) > from those two mirrors (md0 and md1). > > You could also do it the other way: > create two raid0 arrays (disk1a+disk2a=/dev/md0) (disk1b+disk2b=/dev/md1) > then mirror them as /dev/md2. I think that is a nice way to get what I was thinking of. Nice in the way that it is already possible with existing code. But will the mirroring work? Or, if one of the disks fails, can I be sure that the other will have all the data, and that I can recreate the combined md from the two parts? Why has nobody thought of it before? All descriptions I have seen of RAID0+1 says that it needs 4 disks. Best regards keld > > > At 01:53 PM 1/31/2004, Keld Jørn Simonsen wrote: > >Hi! > > > >Is it possible to both do striping and mirroring if you only have 2 disks? > > > >I was thinking of having the chunks organized on each disk so > >that striping reads and writes could be done. Eg. by having > > > >disk1: chunk0 chunk2 chunk4 ...... chunk1 chunk3 chunk5 > >disk2: chunk1 chunk3 chunk5 ...... chunk0 chunk2 chunk4 > > > >Would such a layout of chunks allow for striped reading and writing? > > > >Best regards > >keld > >- > >To unsubscribe from this list: send the line "unsubscribe linux-raid" in > >the body of a message to majordomo@vger.kernel.org > >More majordomo info at http://vger.kernel.org/majordomo-info.html > - To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
