On Fri, May 30, 2014 at 1:14 PM, Mark Knecht <markknecht@xxxxxxxxx> wrote: > On Fri, May 30, 2014 at 12:29 PM, L.M.J <linuxmasterjedi@xxxxxxx> wrote: >> Le Fri, 30 May 2014 12:04:07 -0700, >> Mark Knecht <markknecht@xxxxxxxxx> a écrit : >> >>> In a RAID1 would a 3-drive Red >>> RAID1 possibly be faster than the 2-drive Se RAID1 and at the same >>> time give me more safety? >> >> Just a question inside the question : how do you manager a RAID1 with 3 drives ? Maybe you're talking about >> RAID5 then ? > > OK, I'm no RAID expert but RAID1 is just drives in parallel right. 2 > drives, 3 drives, 4 drives, all holding exactly the same data. In the > case of a 3-drive RAID1 - if there is such a beast - I could safely > lose 2 drives. You ask a reasonable question though as maybe the way > this is actually done is 2 drives + a hot spare in the box that gets > sync'ed if and only if one drive fails. Not sure and maybe I'm totally > wrong about that. > > A 3-drive RAID5 would be 2 drives in series - in this case making 6TB > - and then the 3rd drive being the redundancy. In the case of a > 3-drive RAID5 I could safely lose 1 drive. > > In my case I don't need more than 3TB, so an option would be a 3-drive > RAID5 made out of 2TB drives which would give me 4TB but I don't need > the space as much as I want the redundancy and I think RAID5 is slower > than RAID1. Additionally some more mdadm RAID knowledgeable people on > other lists say Linux mdadm RAID1 would be faster as it will get data > from more than one drive at a time. (Or possibly get data from which > ever drive returns it the fastest. Not sure.) > > I believe one good option if I wanted 4 physical drives would be > RAID10 but that's getting more complicated again which I didn't really > want to do. > > So maybe it is just 2 drives and the 3 drive version isn't even a > possibility? Could be. Using the instructions here: http://sempike.blogspot.com/2012/06/linux-software-raid-mdadm-with-virtual.html I just built a 3 device RAID1 using loop devices and it seems to have worked. Below md50 did not exist, I created it as a 3 device RAID1 and then mdadm shows it's there. I have no idea if it's a good thing to do but mdadm doesn't stop me. I would need to test other real things like putting a file system on it, mounting it, etc., to be more confident but this much seems to work fine. Great question and good experience for me doing this. Thanks! Cheers, Mark c2RAID6 loopraid # cat /proc/mdstat Personalities : [linear] [raid0] [raid1] [raid10] [raid6] [raid5] [raid4] md3 : active raid6 sdb3[9] sdf3[5] sde3[6] sdd3[7] sdc3[8] 1452264480 blocks super 1.2 level 6, 16k chunk, algorithm 2 [5/5] [UUUUU] unused devices: <none> c2RAID6 loopraid # mdadm --create /dev/md50 --level=1 --raid-devices=3 /dev/loop[012] mdadm: Note: this array has metadata at the start and may not be suitable as a boot device. If you plan to store '/boot' on this device please ensure that your boot-loader understands md/v1.x metadata, or use --metadata=0.90 Continue creating array? y mdadm: Defaulting to version 1.2 metadata mdadm: array /dev/md50 started. c2RAID6 loopraid # cat /proc/mdstat Personalities : [linear] [raid0] [raid1] [raid10] [raid6] [raid5] [raid4] md50 : active raid1 loop2[2] loop1[1] loop0[0] 20416 blocks super 1.2 [3/3] [UUU] md3 : active raid6 sdb3[9] sdf3[5] sde3[6] sdd3[7] sdc3[8] 1452264480 blocks super 1.2 level 6, 16k chunk, algorithm 2 [5/5] [UUUUU] unused devices: <none> c2RAID6 loopraid # -- 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
