On Fri, Aug 21, 2009 at 06:43:28PM +0200, Goswin von Brederlow wrote: > Info@xxxxxxxxxxxxxxx writes: > > > Hello list, > > > > Researching RAID10, trying to learn the most advanced system for a 2 > > SATA drive system. Have two WD 2TB drives for a media computer, and > > the most important requirement is data redundancy. I realize that > > RAID is no substitute for backups, but this is a backup for the > > backups and the purpose here is data safety. The secondary goal is > > speed enhancement. It appears that RAID10 can give both. > > > > First question is on layout of RAID10. In studying the man pages it > > seems that Far mode gives 95% of the speed of RAID0, but with > > increased seek for writes. And that Offset retains much of this > > benefit while increasing efficiency of writes. What should be the > > preference, Far or Offset? Are they equally as robust? > > All raid10 layouts offer the same robustness. Which layout is best for > you really depends on your use case. Probably the biggest factor will > be the average file size. My experience is that with large files the > far copies do not cost noticeable write speed while being twice as > fast reading as raid1. The file system elevator makes up for the Far write head movement. > > How safe is the data in Far or Offset mode? If a drive fails, will > > a complete, usable, bootable system exist on the other drive? > > (These two are the only drives in the system, which is Debian > > Testing, Debian kernel 2.6.30-5) Need I make any special Grub > > settings? > > I don't think lilo or grub1 can boot from raid10 at all with offset or > far copies. With near copies you are identical to a simple raid1 so > that would boot. there is a howto on setting up a system, that can continue runnig, if one disk fails at http://linux-raid.osdl.org/index.php/Preventing_against_a_failing_disk > > How does this look: > > # mdadm --create /dev/md0 --level=raid10 --layout=o2 --metadata=1.2 --chunk=64 --raid-disks=2 missing /dev/sdb1 > > On partitions it is save to use 1.1 format. Saves you 4k. Jupey. > > You should play with the chunksize though and try with and without > bitmap and different bitmap sizes. Bitmap costs some write performance > but it greatly speeds up resyncs after a crash or temporary drive > failure. I would recommend a bigger chunk size. at least 256 kiB. Best regards keld -- 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
