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 <alex@xxxxxxxxxxx> wrote:
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.
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
Try:
dd if=ddbenchfile of=- bs=8K | dd if=- of=/dev/null bs=8K
--
Alex Bligh
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