----- Forwarded message from "John A. Sullivan III" <jsulli...@opensourcedevel.com> -----
From: "John A. Sullivan III" <jsulli...@opensourcedevel.com> Date: Sat, 06 Aug 2011 16:30:04 -0400 To: vser...@list.linux-vserver.org Subject: Re: [vserver] hybrid zfs pools as iSCSI targets for vserver Reply-To: vser...@list.linux-vserver.org X-Mailer: Evolution 2.30.3 On Sat, 2011-08-06 at 21:40 +0200, Eugen Leitl wrote: > I've recently figured out how to make low-end hardware (e.g. HP N36L) > work well as zfs hybrid pools. The system (Nexenta Core + napp-it) > exports the zfs pools as CIFS, NFS or iSCSI (Comstar). > > 1) is this a good idea? > > 2) any of you are running vserver guests on iSCSI targets? Happy with it? > Yes, we have been using iSCSI to hold vserver guests for a couple of years now and are generally unhappy with it. Besides our general distress at Nexenta, there is the constraint of the Linux file system. Someone please correct me if I'm wrong because this is a big problem for us. As far as I know, Linux file system block size cannot exceed the maximum memory page size and is limited to no more than 4KB. iSCSI appears to acknowledge every individual block that is sent. That means the most data one can stream without an ACK is 4KB. That means the throughput is limited by the latency of the network rather than the bandwidth. Nexenta is built on OpenSolaris and has a significantly higher internal network latency than Linux. It is not unusual for us to see round trip times from host to Nexenta well upwards of 100us (micro-seconds). Let's say it was even as good as 100us. One could send up to 10,000 packets per second * 4KB = 40MBps maximum throughput for any one iSCSI conversation. That's pretty lousy disk throughput. Other than that, iSCSI is fabulous because it appears as a local block device. We typically mount a large data volume into the VServer host and the mount rbind it into the guest file systems. A magically well working file server without a file server or the hassles of a network file system. Our single complaint other than about Nexenta themselves is the latency constrained throughput. Any one have a way around that? Thanks - John ----- End forwarded message ----- -- Eugen* Leitl <a href="http://leitl.org";>leitl</a> http://leitl.org ______________________________________________________________ ICBM: 48.07100, 11.36820 http://www.ativel.com http://postbiota.org 8B29F6BE: 099D 78BA 2FD3 B014 B08A 7779 75B0 2443 8B29 F6BE _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
