On Thursday December 15, tobias.hofmann@xxxxxxxxxxxxxxxxxxxx wrote: > <delurk> > > On 15.12.2005 21:46, Brad Campbell wrote: > > Callahan, Tom wrote: > > > >> It is always wise to build in a spare however, that being said about all > >> raid levels. In your configuration, if a disk fails in your RAID5, your > >> array will go down. RAID5 is usually 3+ disks, with a mirror. So you > >> should > >> have 3 disks at minimum, and then a 4th as a spare. > > > > /me wonders in the days of reliable RAID-6 why we use RAID-5 + spare? > > Me too. ;) So, with holidays ahead, two questions (as I might tackle > that soon and have not found it mentioned): > > - How would one "switch" from the latter to the former? Is there > something like "grow_to_RAID_6"? No... at least not yet.... > - Does RAID6 have disadvantages wrt write speed? Probably. I haven't done any measurements myself, but from a theoretical standpoint, you would expect raid6 to impose more CPU load (though that may not be noticeable) and as raid6 need to see the whole stripe to update the P and Q blocks (it cannot do a subtract old, add new update) there could well be more IO happening, particularly on large arrays (>5 devices). Of course, whether this caused noticeable reduction in throughput and latency would be very workload-dependant. NeilBrown - 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
