t...@panix.com (Thor Lancelot Simon) writes: >It probably has to do with our small maximum transfer size. The disk is >probably trying to be safer and *not* caching tagged writes as aggressively, >but with only 32 commands in-flight (SCSI/SAS allow 256) and a maximum >transfer size of 64K (our MAXPHYS), that's only 2MB of in-flight data; >maybe not enough to keep up with the actual bandwidth of the media at >its real latency.
With a larger MAXPHYS there wouldn't be as many transfers in flight. The disk here in the Thinkpad behaves differently. With up to 5 concurrent transfers (320k buffer size for dd reading the raw partition) everything is fine. With 6 concurrent transfers the speed goes down again, with 30 transfers we are at half speed. -- -- Michael van Elst Internet: mlel...@serpens.de "A potential Snark may lurk in every tree."