This discussion intrigues me. I think there is a lot of merit to running a raid in this manner. However, if I understand correctly, under normal circumstances reads from a Raid1 md device will always round-robin between the devices to increase performance. Is there a way or what would need to be done to set a single component in the device to be the primary. ie. don't read from the other device unless the first one fails. I think there was some discussion about this a month or so ago concerning ramdisk(which I don't know would be quite as useful), but the theory can apply to any block devices with significantly different speed/latencies, etc. Please advise. --David Dougall On Wed, 29 Jun 2005, Bill Davidsen wrote: > On Wed, 29 Jun 2005, Christopher Smith wrote: > > > > Personally, I wouldn't mess with iSCSI or GNBD. You don't need GNBD in > > > this scenario anyway; simple nbd (which is in the mainline kernel...get > > > the userland tools at sourceforge.net/projects/nbd) will do just fine, > > > and I'd be willing to bet that it is more stable and faster... > > > > I'd briefly tried nbd, but decided to look elsewhere since it needed to > > much manual configuration (no included rc script, /dev nodes appear to > > have to be manually created - yes, I'm lazy). > > Based on one test of nbd, it seems to be stable. I did about what you are > trying, a RAID1 to create an md device, then did an encrypted filesystem > on it. My test was minor, throw a lot of data at it, check that it is > there (md5sum), reboot and verify everything still works, drop the local > drive and rebuild. I did NOT try a rebuild on the nbd drive. > > > > > I've just finished trying NBD now and it seems to solve both my problems > > - rebuild speed is a healthy 40MB/sec + and the failures are dealt with > > "properly" (ie: the md device goes into degraded mode if a component nbd > > suddenly disappears). This looks like it might be a goer for the disk > > node/RAID-over-network back-end. > > I failed it manually, can't say what pulling the plug will do. Glad it's > working, I may be doing this on a WAN in the fall. > > -- > bill davidsen <davidsen@xxxxxxx> > > - > To unsubscribe from this list: send the line "unsubscribe linux-raid" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > 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@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
