Other Cool ZFS Features

There are many items that we have not touched on in this article, and those are worthy of mentioning at this time simply because they are enterprise features that are available with OpenSolaris and with Nexenta.  These are features that the Promise M610i cannot compete with in any way.

Block Level Deduplication - ZFS can employ block level deduplication, which is to say it can detect identical blocks, and simply keep one copy of the data.  This can significantly reduce storage costs, and possibly improve performance when the circumstances allow.  One group that recently deployed a Nexenta instance had originally configured the system for 2TB of storage.  They were using 1.4TB at the time and wanted to have room to grow.  By enabling deduplication they were able to shrink the actual used space on the drives to just under 800GB.  This also has implications when randomly accessing data.  If you have multiple copies of the same data spread out all over a hard drive, it has to seek to find that data.  If it's actually only stored in one place, you can potentially reduce the number of seeks that your drives have to do to retrieve the data.

Compression - ZFS also offers native compression similar to gzip compression.  This allows you to save space at the expense of CPU and memory usage.  For a system that is simply used for archiving data, this could be a great money and space saver.  For a system that is being actively used as a database server, compression may not be the best idea.

Snapshot Shipping - OpenSolaris and Nexenta also offer snapshot shipping.  This allows you to snapshot the entire storage array and back it up via SSH to a remote server.  Once you ship the initial snapshot, only incremental data changes are shipped, so you can conserve bandwidth while still replicating your data to a remote location.  Keep in mind that this is not a block level replication, but a point in time snapshot, so as soon as the snapshot is taken, any new data is not shipped to the remote system.

ZFS Features Nexenta
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  • L. - Wednesday, March 16, 2011 - link

    Too bad you already have the 15k drives.

    2) I wanted to say this earlier, but I'm quite confident that SLC is NOT required for a SLOG device, as with current wear leveling, unless you actually write more than <MLC disk capacity> / day there is no way you'll ever need the SLC's extended durability.

    3) Again, MLC SSD's, good stuff

    4) Yes again

    5) not too shabby

    6) Why use 15k or 7k2 rpm drives in the first place

    All in all nice project, just too bad you have to start from used equipment.

    In my view, you can easily trash both your similar system and Anandtech's test system and simply go for what the future is going to be anyway :
    Raid-10 MLC drives, 48+RAM, 4 CPU's (yes those MLC's are going to perform so much faster you will need this - quite a fair chance you'll need AMD stuff on that as 4-socket is their place) and mainly and this is the hardest part, sata 6 Gb/s * many with a controller that can actually handle the bandwidth.

    Overall you'd get a much simpler, faster and cleaner solution (might need to upgrade your networking though to match with the rest).
  • L. - Wednesday, March 16, 2011 - link

    Of course, 6 months later .. .its not the same equation ;) Sorry for the necro
  • B3an - Tuesday, October 5, 2010 - link

    I like seeing stuff like this on Anand. It's a shame it dont draw as much interest as even the poor Apple articles.
  • Tros - Tuesday, October 5, 2010 - link

    Actually, I was just hoping to see a ZFS vs HFS+ comparison for the higher-end Macs. But with the given players (Oracle, Apple), I don't know if the drivers will ever be officially released.
  • Taft12 - Wednesday, October 6, 2010 - link

    Doesn't it? This interests me greatly and judging by the number of comments is as popular as any article about the latest video or desktop CPU tech
  • greenguy - Wednesday, October 6, 2010 - link

    I have to say, kudos to you Anand for featuring an article about ZFS! It is truly the killer app for filesystems right now, and nothing else is going to come close to it for quite some time. What use is performance if you can't automatically verify that your data (and the system files that tells your system how to manipulate that data) was what it was the last time you checked?

    You picked up on the benefits of the SSD (low latency) before anyone else, it is no wonder you've figured out the benefits of ZFS too earlier than most of your compatriots as well. Well done.
  • elopescardozo - Tuesday, October 5, 2010 - link

    Hi Matt,
    Thank you for the extensive report. In your testing results there are a few unexpected results. I find the difference between Nexenta and Open Solaris hard to understand, unless it is due to misalignment of the IO in the case of Nexenta.
    A zvol (the basis for an iSCSI volume) is created on top of the ZFS pool with a certain block size. I believe the default is 8kB. Next you initialize the volume and format it with NTFS. By default the NTFS structure starts at sector 63 (sixty three, not a typo!), which means that every other 4kB cluster (the NTFS allocation size) falls over a zvol block boundary. That has a serious impact on performance. I saw a report of 70% improvement after properly alignment.
    Is it possible that the Open Solaris and Nexenta pools were different in this respect, either because of different zvol block size (e.g. 8kB for Nexenta, 128kB for Open Solaris – larger blocks means less “boundary cases”) or differences in how the volumes were initialized and formatted?
  • mbreitba - Tuesday, October 5, 2010 - link

    It's possible that the sector alignment could be a problem, but I believe the build that we tested, the default sector size was set to 128kB, which was identical to OpenSolaris. If that has changed, then we should re-test with the newest build to see if that makes any differences.
  • cdillon - Tuesday, October 5, 2010 - link

    Windows Server 2008 aligns all newly created partitions at 1MB, so his NTFS block access should have been properly aligned by default.
  • Mattbreitbach - Tuesday, October 5, 2010 - link

    I was unaware that Windows 2008 correctly aligned NTFS partitions now. Thanks for the info!

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