2009/7/30 Keld Jørn Simonsen <keld@xxxxxxxx>: > I think raid10,f2 only degrades 10-20 % while raid1 can degrade as much > as 50 %. For writing it is about the same, given that you use a file > system on top of the raid. Has anyone done any benchmarks of near vs far setups? >From what I understand, here's how performance should go for a 2-disk raid10 setup: Streaming/large reads far: Up to 100% faster since reads are striped across both disks Streaming/large reads near: Same as single disk as reads can't be striped across both disks Streaming/large writes far: Slower than single disk, since disks have to seek to write. How much of a hit in performance will depend on chunk size. Streaming/large writes near: Same as single disk. Random/small reads far: Up to 100% faster Random/small reads near: Up to 100% faster Random/small writes far: Same as single disk. Random/small writes near: Same as single disk. So basically, if you have a setup which mostly reads from disk, using a far layout is beneficial, but if you have a setup which does a higher percentage of writes, sticking to a near layout will be faster. I recently set up an 8-disk RAID10 across 8 7200 disks across 3 controllers. 5 disks are in an external enclosure via eSATA and a PCIe card. 2 disks are using onboard SATA controller 1 disk is using onboard IDE controller I debated whether or not to use near or far, but ultimately stuck with near for two reasons: 1. The array mostly sees write activity, streaming reads aren't that common. 2. I can only get about 120 MB/s out of the external enclosure because of the PCIe card [1] , so being able to stripe reads wouldn't help get any extra performance out of those disks. -Dave [1] http://ata.wiki.kernel.org/index.php/Hardware,_driver_status#Silicon_Image_3124 -- 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
