If you are in the IT field, you have no doubt heard a lot of great things about ZFS, the file system originally introduced by Sun in 2004.  The ZFS file system has features that make it an exciting part of a solid SAN solution.  For example, ZFS can use SSD drives to cache blocks of data.  That ZFS feature is called the L2ARC.  A ZFS file system is built on top of a storage pool made up of multiple devices.  A ZFS file system can be shared through iSCSI, NFS, and CFS/SAMBA. 

We need a lot of reliable storage to host low cost websites at No Support Linux Hosting.  In the past, we have used Promise iSCSI solutions for SAN based storage.  The Promise SAN solutions are reliable, but they tend to run out of disk IO long before they run out of disk space.  As a result, we have been intentionally under-utilizing our current SAN boxes.  We decided to investigate other storage options this year in an effort to improve the performance of our storage without letting costs get completely out of hand.

We decided to spend some time really getting to know OpenSolaris and ZFS.  Our theory was that we could build a custom ZFS based server for roughly the same price as the Promise M610i SAN, and the ZFS based SAN could outperform the M610i at that price point.  If our theory proved right, we would use the ZFS boxes in future deployments.  We also tested the most popular OpenSolaris based storage solution, Nexenta, on the same hardware.  We decided to blog about our findings and progress at ZFSBuild.com, so others could benefit from anything we learned throughout the project.

ZFS Features
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  • MGSsancho - Tuesday, October 5, 2010 - link

    I haven't tried this myself yet but how about using 8kb blocks and using jumbo frames on your network? possibly lower through padding to fill the 9mb packet in exchange for lower latency? I have no idea as this is just a theory. dudes in the #opensolaris irc chan have always recommended 128K or 64K depending on the data.
  • solori - Wednesday, October 20, 2010 - link

    One easy way to check this would be to export the pool from OpenSolaris and directly import it to NexentaStor and re-test. I think you'll find that the differences - as your benchmarks describe - are more linked to write caching at the disk level than partition alignment.

    NexentaStor is focused on data integrity, and tunes for that very conservatively. Since SATA disks are used in your system, NexentaStor will typically disable disk write cache (write hit) and OpenSolaris may typically disable device cache flush operations (write benefit). These two feature differences can provide the benchmark differences you're seeing.

    Also, some "workstation" tuning includes the disabling of ZIL (performance benefit). This is possible - but not recommended - in NexentaStor but has the side effect of risking application data integrity. Disabling the ZIL (in the absence of SLOG) will result in synchronous writes being committed only with transaction group commits - similar performance to having a very fast SLOG (lots of ARC space helpful too).
  • fmatthew5876 - Tuesday, October 5, 2010 - link

    I'd be very interested to see how FreeBSD ZFS benchmark results would compare to Nexenta and Open Solaris.
  • mbreitba - Tuesday, October 5, 2010 - link

    We have benchmarked FreeNAS's implimentation of ZFS on the same hardware, and the performance was abysmal. We've considered looking into the latest releases of FreeBSD but have not completed any of that testing yet.
  • jms703 - Tuesday, October 5, 2010 - link

    Have you benchmarked FreeBSD 8.1? There were a huge number of performance fixes in 8.1.

    Also, when was this article written? OpenSolaris was killed by Sun on August 13th, 2010.
  • mbreitba - Tuesday, October 5, 2010 - link

    There was a lot of work on this article just prior to the official announcement. The development of the Illumos foundation and subsequent OpenIndiana has been so rapidly paced that we wanted to get this article out the door before diving in to OpenIndiana and any other OpenSolaris derivatives. We will probably add more content talking about the demise of OpenSolaris and the Open Source alternatives that have started popping up at a later date.
  • MGSsancho - Tuesday, October 5, 2010 - link

    Not to mention that projects like illumos are currently not recommended for production, Currently only meant as a base for other distros (OpenIndiana.) Then there is Solaris 11 due soon. I'll try out the express version when its released.
  • cdillon - Tuesday, October 5, 2010 - link

    FreeNAS 0.7.x is still using FreeBSD 7.x, and the ZFS code is a bit dated. FreeBSD 8.x has newer ZFS code (v15). Hopefully very soon FreeBSD 9.x will have the latest ZFS code (v24).
  • piroroadkill - Tuesday, October 5, 2010 - link

    This is relevant to my interests, and I've been toying with the idea of setting up a ZFS based server for a while.

    It's nice to see the features it can use when you have the hardware for it.
  • cgaspar - Tuesday, October 5, 2010 - link

    You say that all writes go to a log in ZFS. That's just not true. Only synchronous writes below a certain size go into the log (either built into the pool, or a dedicated log device). All writes are held in memory in a transaction group, and that transaction group is written to the main pool at least every 10 seconds by default (in OpenSolaris - it used to be 30 seconds, and still is in Solaris 10 U9). That's tunable, and commits will happen more frequently if required, based on available ARC and data churn rate. Note that _all_ writes go into the transaction group - the log is only ever used if the box crashes after a synchronous write and before the txg commits.

    Now for the caution - you have chosen SSDs for your SLOG that don't have a backup power source for their on board caches. If you suffer power loss, you may lose data. Several SLC SSDs have recently been released that have a supercapacitor or other power source sufficient to write cache data to flash on power loss, but the current Intel like up doesn't have it. I believe the next generation Intel SSDs will.

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