On Nov 20, 2007 10:40 AM, Andrew Wilson <[EMAIL PROTECTED]> wrote: > > What kind of workload are you running. If you are you doing these > measurements with some sort of "write as fast as possible" microbenchmark,
Oracle database with blocksize 16K .. populating the database as fast I can > once the 4 GB of nvram is full, you will be limited by backend performance > (FC disks and their interconnect) rather than the host / controller bus. > > Since, best case, 4 gbit FC can transfer 4 GBytes of data in about 10 > seconds, you will fill it up, even with the backend writing out data as fast > as it can, in about 20 seconds. Once the nvram is full, you will only see > the backend (e.g. 2 Gbit) rate. > > The reason these controller buffers are useful with real applications is > that they smooth the bursts of writes that real applications tend to > generate, thus reducing the latency of those writes and improving > performance. They will then "catch up" during periods when few writes are > being issued. But a typical microbenchmark that pumps out a steady stream of > writes won't see this benefit. > > Drew Wilson > > > > Asif Iqbal wrote: > On Nov 20, 2007 7:01 AM, Chad Mynhier <[EMAIL PROTECTED]> wrote: > > > On 11/20/07, Asif Iqbal <[EMAIL PROTECTED]> wrote: > > > On Nov 19, 2007 1:43 AM, Louwtjie Burger <[EMAIL PROTECTED]> wrote: > > > On Nov 17, 2007 9:40 PM, Asif Iqbal <[EMAIL PROTECTED]> wrote: > > > (Including storage-discuss) > > I have 6 6140s with 96 disks. Out of which 64 of them are Seagate > ST3300007FC (300GB - 10000 RPM FC-AL) > > Those disks are 2Gb disks, so the tray will operate at 2Gb. > > > That is still 256MB/s . I am getting about 194MB/s > > 2Gb fibre channel is going to max out at a data transmission rate > > But I am running 4GB fiber channels with 4GB NVRAM on a 6 tray of > 300GB FC 10K rpm (2Gb/s) disks > > So I should get "a lot" more than ~ 200MB/s. Shouldn't I? > > > > > around 200MB/s rather than the 256MB/s that you'd expect. Fibre > channel uses an 8-bit/10-bit encoding, so it transmits 8-bits of data > in 10 bits on the wire. So while 256MB/s is being transmitted on the > connection itself, only 200MB/s of that is the data that you're > transmitting. > > Chad Mynhier > > > > > > > -- Asif Iqbal PGP Key: 0xE62693C5 KeyServer: pgp.mit.edu _______________________________________________ perf-discuss mailing list perf-discuss@opensolaris.org
