[prev in list] [next in list] [prev in thread] [next in thread] 

List:       opensolaris-storage-discuss
Subject:    [storage-discuss] iSCSI Target performance
From:       Rick McNeal <Rick.McNeal () Sun ! COM>
Date:       2007-02-09 1:15:04
Message-ID: A9D22081-53F5-45C8-A389-17B69F77734F () Sun ! COM
[Download RAW message or body]

If anyone is doing some simple I/O tests, like dd, for example with  
iSCSI and noticing abysmal performance I just found something.  
Internally someone was setting up a machine with iSCSI and noticed  
the following:

time dd if=<iscsi_target> of=/dev/null bs=1k count=200

    reported time would be 12 seconds.

time dd if=<iscsi_target> of=/dev/null bs=8k count=200

    reported time would be less than a second.

For the test the iSCSI target backing store was a file in /tmp, so  
it's a ram disk. The link between the two machines is a 10GbE.

Clearly something odd was happening since there's no way 1k reads  
should be slower than 8k reads. Well, after poking around a little  
bit it turns out this simple test case is showing why the "Nagele  
Algorithm" is not a good fit for iSCSI. By disabling this feature the  
times for the 1KB case are just a fraction of a second quicker than  
the 8KB which is expected.

I just wanted to point this out to folks in case you've noticed the  
problem and where wondering why or saw this problem and thought the  
Solaris iSCSI Target was a piece of junk. I'll be fixing this with my  
next set of changes.
----
Rick McNeal

"If ignorance is bliss, this lesson would appear to be a deliberate  
attempt on your part to deprive me of happiness, the pursuit of which  
is my unalienable right according to the Declaration of  
Independence.  I therefore assert my patriotic prerogative not to  
know this material.  I'll be out on the playground." -- Calvin


_______________________________________________
storage-discuss mailing list
storage-discuss@opensolaris.org
http://mail.opensolaris.org/mailman/listinfo/storage-discuss
[prev in list] [next in list] [prev in thread] [next in thread]