[OpenIndiana-discuss] CIFS slow reads but fast writes

[Dan Swartzendruber]

-----Original Message-----
From: Roy Sigurd Karlsbakk [mailto:roy at karlsbakk.net] 
Sent: Tuesday, April 19, 2011 5:44 AM
To: Discussion list for OpenIndiana
Subject: Re: [OpenIndiana-discuss] CIFS slow reads but fast writes

----- Original Message -----
> Hmmm, just got going on this (had to work late.) Anyway, I'm setting
> up the
> iscsi and cifs shares now, but as an experiment, I did this:
> 
> time dd of=/dev/null if=testfile bs=1M count=16K
> 
> write speed = 322 MB/s
> 
> then did this:
> 
> root at nas:/tank/smbtest# time dd of=/dev/null if=testfile bs=1M
> count=16K
> 
> read speed = 412 MB/s
> 
> seems like this lets disk/fs off the hook, no?

I'd use a real benchmark utility instead of just dd. Aslo keep in mind that
this test won't do much i/o if you have compression enabled. CIFS may or may
not use SYNC writes, iSCSI will (normally) use SYNC writes, so that will
have some impact, but for reads, they shouldn't matter. In most (or all?)
circumstances, reads should be faster than writes.

**** For what it's worth, I disabled sync before doing any of the tests.  No
compression involved.  The crystaldiskmark test I was doing does sequential
reads and then sequential writes, which I thought would be reasonably
modeled by 'dd'.