On 7 Jan 2010 at 9:52, Jack Z wrote: [...] > Based on these numbers, it seems that the receiver has realized the > large bandwidth and long RTT character of the link and advertised a > big window; however, the sender, i.e. the iSCSI initiator, seems not > to take the advantage of this. Do you maybe have any idea about why? > [...]
After all, it's still SCSI: The OS will not send an arbitrary number of requests (which would be TCP segments) unless previous requests have been answered. One of the reasons may be write ordering of data and metadata. An interesting correlation would be the size of the SCSI tagged queue size and the number of unanswered requests in case of massive random read (or write) operations. I know that the host driver of the Adaptec aic7xxx could display the maximum queue size as well as the used queue size, but I haven't checked for iSCSI (I'm not using an Adaptec HBA any more). Regards, Ulrich
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