That dd give me this. dd if=ddbenchfile of=- bs=8K | dd if=- of=/dev/null bs=8K 8192000000 bytes (8.2 GB) copied, 31.1807 s, 263 MB/s
Which makes sense because the SSD is running as SATA 2 which should give 3Gbps or ~300MBps I am still trying to better understand the speed difference between the small block speeds seen with dd vs the same small object size with rados. It is not a difference of a few MB per sec. It seems to nearly be a factor of 10. I just want to know if this is a hard limit in Ceph or a factor of the underlying disk speed. Meaning if I use spindles to read data would the speed be the same or would the read speed be a factor of 10 less than the speed of the underlying disk? On Wed, Sep 18, 2013 at 4:27 AM, Alex Bligh <a...@alex.org.uk> wrote: > > On 17 Sep 2013, at 21:47, Jason Villalta wrote: > > > dd if=ddbenchfile of=/dev/null bs=8K > > 8192000000 bytes (8.2 GB) copied, 19.7318 s, 415 MB/s > > As a general point, this benchmark may not do what you think it does, > depending on the version of dd, as writes to /dev/null can be heavily > optimised. > > Try: > dd if=ddbenchfile of=- bs=8K | dd if=- of=/dev/null bs=8K > > -- > Alex Bligh > > > > > -- -- *Jason Villalta* Co-founder [image: Inline image 1] 800.799.4407x1230 | www.RubixTechnology.com<http://www.rubixtechnology.com/>
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