DragonFly users List (threaded) for 2009-06
DragonFly BSD
DragonFly users List (threaded) for 2009-06
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Re: dragonfly- UFS + HAMMER + mirroring setup designed instead of RAID - Is this OK?

From: Matthew Dillon <dillon@xxxxxxxxxxxxxxxxxxxx>
Date: Thu, 25 Jun 2009 10:22:35 -0700 (PDT)

:Thanks for the info Dillon on the pfs naming convention and idea about
:mirror stream.
:Since you recommended SSDs before I tried to get them from vendors I
:know but most of them haven't even heard about it ( I am from Kerala,
:India ).
:Will a USB Flash drive serve the same purpose?
:Something like.
:Are they as reliable as the SATA SSD you mentioned. it is available
:with the vendors ( 8GB )

    No, USB-connected storage is just not reliable due to the protocol,
    and USB flash drives are doubly unreliable because they do not use
    good wear-leveling algorithms.  If you want a SSD which has
    the same MTBF as the motherboard (hence justifying that only one is
    needed, with no other redundancy), it has to be an internal SATA SSD.

    Here are some examples:


    SSD units are very expensive per gigabyte, but as a root disk you only
    need a few gigabytes of space.  Even 16G or 32G is plenty big enough.
    So, e.g. the 30G OCZ Vertex would be plenty big enough.

    The only issue with SSD storage is that you don't want to be continuously
    writing to it.  The less writing you do the more bullet proof it becomes
    as a boot+root disk.  Depending on the situation you can put /tmp and
    /var/tmp on, say, a memory fs (via md or mfs), and other mass-use
    temporary space such as /usr/obj on either the real hard drive or over
    NFS.  Swap is a little more difficult.  You'd either run without swap
    configured or you would put it on the real hard drive.  DragonFly will
    in fact run just fine with no swap configured if you have enough memory.
    It's very well tuned for that.

    For larger SSDs, like the 128G's it takes much longer for the wear
    to matter (because it has more space to spread the wear out on) and both
    the temporary and swap space can be put on the SSD.

					Matthew Dillon 

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