On Jun 7, 2010, at 11:06 AM, Miles Nordin wrote: > > the other difference is in the latest comstar which runs in > sync-everything mode by default, AIUI. Or it does use that mode only > when zvol-backed? Or something.
It depends on your definition of "latest." The latest OpenSolaris release is 2009.06 which treats all Zvol-backed COMSTAR iSCSI writes as sync. This was changed in the developer releases in summer 2009, b114. For a release such as NexentaStor 3.0.2, which is based on b140 (+/-), the initiator's write cache enable/disable request is respected, by default. >>>> * Should I go with fiber channel, or will the 4 built-in 1Gbe >>>> NIC's give me enough speed? > > FC has different QoS properties than Ethernet because of the buffer > credit mechanism---it can exert back-pressure all the way through the > fabric. same with IB, which is HOL-blocking. This is a big deal with > storage, with its large blocks of bursty writes that aren't really the > case for which TCP shines. Please don't confuse Ethernet with IP. Ethernet has no routing and no back-off other than that required for the link. Since GbE and higher speeds are all implemented as switched fabrics, the ability of the switch to manage contention is paramount. You can observe this on a Solaris system by looking at the NIC flow control kstats. For a LAN environment, there is little practical difference between Ethernet and FC wrt port contention -- high quality switches will prove better than bargain-basement switches, with direct attach (no switches) being the optimum cost+performance solution. WANs are a different beast, and is where we find tuning the FC buffer credits to be worth the effort. For WANs no tuning is required for IP on modern OSes (Ethernet doesn't do WAN). > I would try both and compare, if you can > afford it! +1 -- richard -- ZFS and NexentaStor training, Rotterdam, July 13-15, 2010 http://nexenta-rotterdam.eventbrite.com/ _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
