Michael Tokarev writes: : Dean S. Messing wrote: : [] : > [] That's what : > attracted me to RAID 0 --- which seems to have no downside EXCEPT : > safety :-). : > : > So I'm not sure I'll ever figure out "the right" tuning. I'm at the : > point of abandoning RAID entirely and just putting the three disks : > together as a big LV and being done with it. (I don't have quite the : > moxy to define a RAID 0 array underneath it. :-) : : "Putting three disks together as a big LV" - that's exactly what : "linear" md module. : It's almost as unsafe as raid0, but with : linear read/write speed equal to speed of single drive... I understand I only get the speed of a single drive was I was not aware of the safety factor. I had intended to use snapshotting off to a cheap USB drive each evening. Will that not keep me safe within a day's worth of data change? I only learned about "snapshots" yesterday. I'm utterly new to the disk array/LVM game. For that matter why not run a RAID-0 + LVM across two of the three drives and snapshot to the third? : Note also that the more drives you add to raid0-like config, : the more chances of failure you'll have - because raid0 fails : when ANY drive fails. Ditto - for certain extent - for linear : md module and for "one big LV" which is basically the same thing. I understand the probability increases for additional drives. : By the way, before abandoming "R" in "RAID", I'd check whenever : the resulting speed with raid5 (after at least read-ahead tuning) : is acceptable, and use that if yes. My problem is not quite knowing what "acceptable" is. I bought a Dell Precision 490 with two relatively fast SATA II drives. With RAID 0 I attain speeds of nearly 140 MB/s (using 2 drives) for reads and writes and the system is very snappy for everything, from processing 4Kx2K video to building a 'locate' datebase, to searching my very large mail archives for technical info. When I see the speed loss of software RAID 5 (writes are at 55MB/s and random reads are at 54 MB/s) for everything but seq. reads (and that only if I increase read-ahead from 512 to 16384 to get read speeds of about 110 MB/s I lose heart, esp. since I don't know the other consequences of increasing read-ahead by so much. : If no, maybe raid10 over : the same 3 drives will give better results. Does RAID10 work on three drives? I though one needed 4 drives, with striping across a pair of mirrored pairs. Dean - 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
