RE: FW: 20TB Storage System

From: Max Clark (max.clark_at_media.net)
Date: 09/02/03

  • Next message: Poul-Henning Kamp: "Re: FW: 20TB Storage System" 
    To: "Poul-Henning Kamp" <phk@phk.freebsd.dk>
Date: Tue, 2 Sep 2003 13:14:58 -0700

    I know adding ccd/vinum to the equation will lower my IO throughput, but the
    question is... if I have an external hardware shelf with 3.5TB (16 250GB
    drives w/ Raid 5 from hardware) and I put a Raid 0 stripe across 3 of these
    shelves what would my expected loss of IO be?

    Thanks,
    Max

    -----Original Message-----
    From: Poul-Henning Kamp [mailto:phk@phk.freebsd.dk]
    Sent: Tuesday, September 02, 2003 1:02 PM
    To: Max Clark
    Cc: freebsd-questions@freebsd.org; freebsd-performance@freebsd.org;
    freebsd-hackers@freebsd.org
    Subject: Re: FW: 20TB Storage System

    In message <ILENIMHFIPIBHJLCDEHKIEMEDCAA.max.clark@media.net>, "Max Clark"
    writ
    es:

    >Given the above:
    >1) What would my expected IO be using vinum to stripe the storage
    enclosures
    >detailed above?

    That depends a lot on the applications I/O pattern, an I doubt a
    precise prediction is possible.

    In particular the FibreChannel is hard to predict the throughput off
    because the various implementations seems to have each their own
    peculiar quirks performance wise.

    On a SEAGATE ST318452 disks, I see sequential transfer rates
    at the outside rim of the disk of 58MB/sec. If I stripe two of
    them them with CCD I get 107MB/sec.

    CCD has a better performance than Vinum where they compare.

    RAID-5 and striping a large number of disks does not scale linearly
    performance wise, in particular you _may_ see your average access
    time drop somewhat, but there is by far no guarantee that it will
    be better than the individual drive.

    >2) What is the maximum size of a filesystem that I can present to the host
    >OS using vinum/ccd? Am I limited anywhere that I am not aware of?

    Good question, I'm not sure we currently know the exact barrier.

    >3) Could I put all 20TB on one system, or will I need two to sustain the IO
    >required?

    Spreading it will give you more I/O bandwidth. 

    --
Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
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