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Thread: ZFS - a file system well worth looking into if you haven't already

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    ZFS - a file system well worth looking into if you haven't already

    As a ZFS noob I am pretty impressed by the feature set. I'm currently experimenting with it on nexentastor community 3.0.x running as a VM on ESXi4.1 and confirming good dedupe ratios holding Virtual machines on an HP microserver.
    From what I understand it's pretty good for data integrity and makes good use of RAM and SSD's as a cache, apart from in one vital area. It can only use 1/4 of your RAM for dedupe metadata as per http://bugs.opensolaris.org/view_bug.do?bug_id=6957289
    Currently, I use 4k blocks as the Windows VM's use 4k (aligned) clusters.
    Unfortuantely, that makes for a large dedupe overhead or a performance hit as SHA256 hashes are 1/128th of the size of the blocks and these must be stored in RAM.
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    Re: ZFS - a file system well worth looking into if you haven't already

    glad you are getting on well with it - I've seen some interesting posts of people running it directly on the micro server with some SSD cache - you have a little bit of a problem with NFS links.

    still I think as a home lab VSA its certainly up there.

    have you tried the EMC Celerra uberVSA?
    my Virtualisation Blog http://jfvi.co.uk Virtualisation Podcast http://vsoup.net

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    Re: ZFS - a file system well worth looking into if you haven't already

    Quote Originally Posted by Moby-Dick View Post
    glad you are getting on well with it - I've seen some interesting posts of people running it directly on the micro server with some SSD cache - you have a little bit of a problem with NFS links.
    I seem to be having problems with the NFS "dropping out" when performing a storage vmotion.
    still I think as a home lab VSA its certainly up there.

    have you tried the EMC Celerra uberVSA?
    Not tried that yet.
    Performance on Nexentastor with less than 2GB assigned to it seems a little low. It isn't using all of the RAM assigned to it, CPU usage for the VM and the Microserver is low, however the CPU wait is 33 Millisecond according to the Vcentre. I've found this figure to be unreliable however as whenever I see high CPU wait figures and then use ESXtop, I get much more reasonable ones. I don't think there's a CPU problem here. Maybe it's just the slow HDD in the microserver.

    Some dedupe figures for anyone interested:
    All VM's are using 4k clusters and are block aligned. This is essential for both performance on any SAN and for any kind of useful dedupe on any file system.
    SHA256 - no verify - no compression - 1 xp 32bit vm moved on to NFS share Dedupe ratio 1.17x
    Last edited by badass; 04-03-2011 at 10:47 AM.
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    Re: ZFS - a file system well worth looking into if you haven't already

    The thing is about dedupe is that its only really going to kick in when you have multiple systems on a volume. the level of dedupe on a given box is not going to be high by default unless you have a lox with a lot of similar data.
    my Virtualisation Blog http://jfvi.co.uk Virtualisation Podcast http://vsoup.net

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    Re: ZFS - a file system well worth looking into if you haven't already

    Quote Originally Posted by Moby-Dick View Post
    The thing is about dedupe is that its only really going to kick in when you have multiple systems on a volume. the level of dedupe on a given box is not going to be high by default unless you have a lox with a lot of similar data.
    That dedupe is for a single bare XP install - IMHO getting nearly 20% of your space back in those circumstances is pretty good.
    I did add another couple of XP VM's and the dedupe predictably shot up. There's also a lot of shared data between Server 2003 and XP and adding another one of those caused the dedupe ratio to go down, howeverit did not add the size of teh 2003 VM to the extra storage space needed. i.e. the dedupe did see shared data between it and the xp machines.
    One thing I have found so far:
    Using the dedupe method verify kills performance. Either just use SHA256 no verify or just use the dedupe for a volume that holds backups.

    At work, we have around 1TB of production data currently. This is a mix of user home folder data etc, databases and virtual machines. Last time I checked, we had around 1 50% saving of data usage due to dedupe.
    If our FAS2020 wasn't artificially castrated by Netapp, chucking in a flash cache and using the dedupe would probably make our virtual infrastructure fly.
    Top tip to anyone looking at Netapp solutions. Do not consider the FAS2020. Its CPU is weak, it doesn't have enough RAM and this prevents it from running the newer Ontap OS whuch has much better vmware integration,
    Last edited by badass; 05-03-2011 at 01:10 PM.
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    Re: ZFS - a file system well worth looking into if you haven't already

    yeah I have a Fas2020 in my lab , it wasn't my first choice for storage , still its connected to a good fabric
    my Virtualisation Blog http://jfvi.co.uk Virtualisation Podcast http://vsoup.net

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    Re: ZFS - a file system well worth looking into if you haven't already

    What about running off-line/batch dedupe, rather than doing it on file creation?

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    Re: ZFS - a file system well worth looking into if you haven't already

    Quote Originally Posted by watercooled View Post
    What about running off-line/batch dedupe, rather than doing it on file creation?
    Netapp can only do offline dedupe and it takes a performance hit as you would expect when it's doing it.
    ZFS is incapable of offline dedupe currently (they call it asynchronous)
    I'd prefer it if they offered asynchronous dedupe as well.
    More dedupe figures: 2 xp machines - they were both made from the same clone.
    2.35x
    I'm going to add another xp machine that was built far earlier that has lots of software on it later and see the effect.
    "In a perfect world... spammers would get caught, go to jail, and share a cell with many men who have enlarged their penises, taken Viagra and are looking for a new relationship."

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