Any other thoughts on this thread guys. I am just crazy to want near native SSD performance on a small SSD cluster?
On Wed, Sep 18, 2013 at 8:21 AM, Jason Villalta <ja...@rubixnet.com> wrote: > 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/> > -- -- *Jason Villalta* Co-founder [image: Inline image 1] 800.799.4407x1230 | www.RubixTechnology.com<http://www.rubixtechnology.com/>
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