Re: Network very very slow... was iSCSI and jumbo frames

[BERTRAND Joël <joel.bertrand%systella.fr@localhost>]

Michael van Elst a écrit :
> On Fri, Feb 05, 2021 at 09:03:28AM +0100, BERTRAND Joël wrote:
>>   LUN0 Storage /dev/dk6 Auto
>>
>> 	I can change dk6 by rdk6, but it's not a solution to fix issue with
>> iscsid, when NetBSD initiator tries to use a iSCSI target. In my case,
>> istgt runs as expected even if I can increase its performance.
> 
> If you use the block device as the iSCSI backend, the data is passed
> through the buffer cache of the host. That's slow for the first
> time, fast for repetitions (since the data is cached) unless it's
> more data than fits into the buffer cache, then it's ugly slow.
> 
> vm.bufcache is 15 (percent) by default. On your 16GB machine
> that means that I/O of up to about 2GB may look fine, but
> if you move more, things will crawl.
> 
> You also get the effect that writing seems to be fine at the start
> as data is only buffered and slowly written out in the background.
> Once the cache fills or isn't yet flushed from a previous run, speed
> drops to very low levels.
> 
> 
> But that doesn't explain anything with your qNAP NAS.

	To be sure that this issue does come from qNAP NAS, I have tried to
replace this initiator by another one (a Linux iscsi initiator) and
result is very similar. That's being said, qNAP runs with a Linux kernel...

	JKB