On Fri, 2015-08-14 at 12:30 -0400, Calvin Walton wrote: > On Fri, 2015-08-14 at 12:16 -0300, Eduardo Bach wrote: > > Hi all, > > > > This is my first email to this list, so please excuse any gaffe. > > > > I am in the evaluation early stages of a new storage, an SGI MIS, > > currently with two HBAs LSI and 32 disks. > > The hba controllers are LSI 9207-8i and the disks are Seagate 6TB, > > model ST6000NM0004-1FT17Z. > > > > To evaluate the performance I am using IOzone over a raid0 using > > all > > the 32 disks, with the parameters: iozone -i0 -i1 -t5 -s 20G -P0. > > > > With btrfs the result approaches 3.5GB/s. When using mdadm+xfs the > > result reaches 6gb/s, which is the expected value when compared > > with > > parallel dd made on discs. > > When used btrfs with only half of the disc the result is about > > 3GB/s. > > There's two things in particular to pay attention with on btrfs with > this sort of setup right now:
Umm, Ok, I made a mistake. You can ignore paragraph #1 - I got some details about the btrfs raid1 and raid0 modes mixed up! Btrfs RAID0 is n-way striping across all available drives which have room for allocations. > 1. btrfs's "raid0" is not an n-way stripe; it's a 2-way stripe > only. (n > -way stripe is a long requested feature, but there is no > timeline on > its completion) A single-threaded disk write will only ever be > writing to two disks at the same time. The total throughput you > get > for multithreaded writes is up to which blocks the allocator > happens > to pick; it will probably often happen that multiple threads > will > both be using the same chunk, sharing IO from only 2 disks. > 2. Btrfs development is currently primarily focused on > functionality > over performance. There's several places where placeholder or > untuned algorithms are used (e.g. the multi-mirror io read > scheduling just does pid % number_of_mirrors to pick a mirror). > > This kind of a performance difference on large performance-oriented > RAID systems between btrfs's built-in raid and mdadm is interesting > to > see, but for the moment I'd say it's mostly expected. > > One of the developers here might have some more precise information > on > exactly why you're seeing such a performance difference. > > As an aside, you have 192TB in RAID0? That's certainly pretty > impressive, but as soon as one disk dies, you're going to lose a > *lot* > of data. > -- Calvin Walton <calvin.wal...@kepstin.ca> -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
