On Thu, May 05, 2011 at 09:26:45AM +0200, David Brown wrote: > On 05/05/2011 02:40, Liam Kurmos wrote: > >Cheers Roberto, > > > >I've got the gist of the far layout from looking at wikipedia. There > >is some clever stuff going on that i had never considered. > >i'm going for f2 for my system drive. > > > >Liam > > > > For general use, raid10,f2 is often the best choice. The only > disadvantage is if you have applications that make a lot of synchronised > writes, as writes take longer (everything must be written twice, and > because the data is spread out there is more head movement). For most > writes this doesn't matter - the OS caches the writes, and the app > continues on its way, so the writes are done when the disks are not > otherwise used. But if you have synchronous writes, so that the app > will wait for the write to complete, it will be slower (compared to > raid10,n2 or raid10,o2). Yes syncroneous writes would be significantly slower. I have not seen benchmarks on it, tho. Which applications typically use syncroneous IO? Maybe not that many. Do databases do that, eg postgresql and mysql? > The other problem with raid10 layout is booting - bootloaders don't much > like it. The very latest version of grub, IIRC, can boot from raid10 - > but it can be awkward. There are lots of how-tos around the web for > booting when you have raid, but by far the easiest is to divide your > disks into partitions: > > sdX1 = 1GB > sdX2 = xGB > sdX3 = yGB > > Put all your sdX1 partitions together as raid1 with metadata layout > 0.90, format as ext3 and use it as /boot. Any bootloader will work fine > with that (don't forget to install grub on each disk's MBR). > > Put your sdX2 partitions together as raid10,f2 for swap. > > Put the sdX3 partitions together as raid10,f2 for everything else. The > most flexible choice is to use LVM here and make logical partitions for > /, /home, /usr, etc. But you can also partition up the md device in > distinct fixed partitions for /, /home, etc. if you want. there is a similar layout of your disks described in https://raid.wiki.kernel.org/index.php/Preventing_against_a_failing_disk > Don't try and make sdX3 and sdX4 groups and raids for separate / and > /home (unless you want to use different raid levels for these two > groups). Your disks are faster near the start (at the outer edge of the > disk), so you get the best speed by making the raid10,f2 from almost the > whole disk. Hmm, I think the root partition actually would have more accesses than /home and other partitions, so it may be beneficial to give the fastest disk sectors to a separate root partition. Comments? 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
