Different workloads can have very different characteristics which makes I/O benchmarks tricky. At one extreme you can have lots of small I/O requests updating a data base where each update writes a small amount of data but also requires updates to tables, indices, etc. Numerical simulations can write large amounts of data as fast as the disks can take it, but will wait for the I/O to finish before making new requests. Video capture (which these days may involve multiple "cameras" and high resolutions) will drop data if the disks can't keep up.
The most useful comparison would be based on whatever elements of your real workload are currently a bottleneck. When you make major changes to your mass storage, there may be opportunities to improve the workflow, e.g., running multiple tasks in parallel, so it can be helpful to have some benchmarks for several variations on the old workflow. At work, moving from SGI multiprocessor systems to Mac Pro, we found that SGI I/O could handle only 2 of our standard workload tasks, which (because we didn't want to slow down interactive users) meant we were limited to one batch process at a time. The Mac Pros start to bog down at around 8 tasks (using 3 disks in a stripped configuration). On Sun, Dec 15, 2013 at 1:46 PM, Dinse, Gregg (NIH/NIEHS) [V] < [email protected]> wrote: > Hi, > > Can someone please recommend some (free?) software that would allow me to > assess read and write speeds for various disks (e.g., hard drives, SSDs, > flash drives)? > > Alternatively, are there some simple commands that I can give in the > Terminal app? At one time, I believe someone gave me such a command, but > unfortunately I have long ago forgotten it. I think the "write" part of > the test involved writing a large amount of stuff to /dev/null. > > In case anyone is interested in the background, I am hoping to use a pair > of PCIe cards to upgrade a mid-2012 Mac Pro by adding some external USB-3 > ports and some internal SATA III ports. I wanted to assess "before and > after" speeds. > > Thanks, > > Gregg > > _______________________________________________ > MacOSX-talk mailing list > [email protected] > http://www.omnigroup.com/mailman/listinfo/macosx-talk > -- George N. White III <[email protected]> Head of St. Margarets Bay, Nova Scotia
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