Re: zfs as layer distributor - FreeBSD

This is a discussion on Re: zfs as layer distributor - FreeBSD ; Dimitar Vasilev wrote: > Hi all, > Does someone use zfs as layer distributor on the top of hardware raid - > (RAID10,RAID6,etc)? I've found ZFS works faster when given more than one disk device. The reason being, it is ...

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Thread: Re: zfs as layer distributor

  1. Re: zfs as layer distributor

    Dimitar Vasilev wrote:
    > Hi all,
    > Does someone use zfs as layer distributor on the top of hardware raid -
    > (RAID10,RAID6,etc)?


    I've found ZFS works faster when given more than one disk device. The
    reason being, it is smart about writing journal logs and metadata copies
    to different devices, resulting in higher performance by using idle
    disks. It also provides more "channels" for write clustering so higher
    throughput on write-heavy loads.

    Secondly if you use ZFS to provide RAID1 or RAID5, due to checksumming
    it can be smarter about which data it chooses in the event of a checksum
    failure. Hardware RAID can only do this with RAID6.

    Finally, when ZFS issues "flush cache" command to the disk for metadata
    and journal logs, there is less data to flush when you give it multiple
    smaller devices. If you have a single monolithic RAID device with a
    large (eg. 256mb) cache, it can ruin performance while the RAID card
    flushes its entire cache. (This can be disabled with a sysctl).

    - Andrew
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  2. Re: zfs as layer distributor

    2008/10/6 Andrew Snow

    > Dimitar Vasilev wrote:
    >
    >> Hi all,
    >> Does someone use zfs as layer distributor on the top of hardware raid -
    >> (RAID10,RAID6,etc)?
    >>

    >
    > I've found ZFS works faster when given more than one disk device. The
    > reason being, it is smart about writing journal logs and metadata copies to
    > different devices, resulting in higher performance by using idle disks. It
    > also provides more "channels" for write clustering so higher throughput on
    > write-heavy loads.
    >
    > Secondly if you use ZFS to provide RAID1 or RAID5, due to checksumming it
    > can be smarter about which data it chooses in the event of a checksum
    > failure. Hardware RAID can only do this with RAID6.
    >
    > Finally, when ZFS issues "flush cache" command to the disk for metadata and
    > journal logs, there is less data to flush when you give it multiple smaller
    > devices. If you have a single monolithic RAID device with a large (eg.
    > 256mb) cache, it can ruin performance while the RAID card flushes its entire
    > cache. (This can be disabled with a sysctl).
    >
    > - Andrew


    Thanks Andrew,
    I have an Areca 1120 with RAID-6 and on the top of it a zfs as a layer
    distributor.
    So far I can tell the following:
    1)works nice and fast
    2)can be pain in the rear if your controller spits one of the disks due to
    power surge/etc.
    3) zfs snapshots caused some crashes and bad descriptors on 7.0-stable as of
    3 months behind- but it's somewhat expected.
    I'm thinking of raidz2 and setting the disks as pass-through.
    Would love if someone to hear if someone has tested hardware raid6 and zfs
    over it.
    Best regards,
    Dimitar
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  3. Re: zfs as layer distributor

    Dimitar Vasilev wrote:
    > Would love if someone to hear if someone has tested hardware raid6 and
    > zfs over it.


    Yes, I am using 3ware RAID6 over 16 disks as a single volume, because we
    also had UFS partitions that we wanted to keep.

    The performance is more than adequate, but not anywhere near if you used
    them as single disks. Personally - based on prior experience with
    certain hardware - I'd trust ZFS software raid over Areca hardware :-)

    How many disks do you have? If you can split up your disk pack into a
    group of between 5 and 10 smaller RAIDs, that is the optimal range for
    ZFS performance.


    - Andrew
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    http://lists.freebsd.org/mailman/listinfo/freebsd-fs
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  4. Re: zfs as layer distributor

    2008/10/6 Andrew Snow

    > Dimitar Vasilev wrote:
    >
    >> Would love if someone to hear if someone has tested hardware raid6 and zfs
    >> over it.
    >>

    >
    > Yes, I am using 3ware RAID6 over 16 disks as a single volume, because we
    > also had UFS partitions that we wanted to keep.
    >
    > The performance is more than adequate, but not anywhere near if you used
    > them as single disks. Personally - based on prior experience with certain
    > hardware - I'd trust ZFS software raid over Areca hardware :-)
    >
    > How many disks do you have? If you can split up your disk pack into a group
    > of between 5 and 10 smaller RAIDs, that is the optimal range for ZFS
    > performance.
    >
    >
    > - Andrew


    I got 8 disks out of 12 possible.
    As the local reps of Areca told me - RAID6 is good over 12 disks.
    So next time I think I will go with raidz2 and pass-through.
    Best regards,
    Dimitar
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