Re: Very low disk performance on 5.x

From: Bakul Shah (bakul_at_BitBlocks.com)
Date: 05/02/05

  • Next message: Steven Hartland: "Re: Very low disk performance on 5.x" 
    To: "Poul-Henning Kamp" <phk@phk.freebsd.dk>
Date: Mon, 02 May 2005 11:27:03 -0700

    It may make sense to look at measured bandwidth as a
    percentage of *guaranteed not to exceed* bandwidth of the
    disk setup -- what is the theoretical max bandwidth writing
    to a raw partition (and assuming zero cpu overhead, latency,
    seek time)? This will help in figuring out how to maximize
    end-to-end performance, taking into account filesystem
    overhead, data integrity tradeoffs etc. One has to measure
    each component to find and fix the top N bottlenecks. This
    sort of critical analysis is what allowed people to make
    TCP/IP blazingly fast.

    For instance, Hartland reported max read/write performance of
    about 260M/s. *If* his disks can do, say, 80MB/s, for a 5
    disk RAID5 he'd get 320MB/s. If so, his end-to-end measured
    performance would be over 80% of max (for whatever data
    integrity guarantees). Not too shabby:-)

    Improving end-to-end disk/os/filesystem performance can be
    quite an exciting (and time consuming) project.
    - do we have hooks to measure performance of each component?
    - do we have tests for these?
    - do we know the top 3 bottlenecks?
    - do we have a framework for independently experimenting
      with each component? (geom definitely helps here!)
    - do we have a framework for experimenting with various
      filesystem layout schemes? with various caching
      strategies? with various allocation strategies?
    - tools for locating bottlenecks due to mistuning?
    - tools to help tune the system?
    - how about tools to auto-tune the system?:)

    I agree with the questions you raised, but it seems we need
    to move the discussion to a meta level! I fully realize that
    in a volunteer project a) there are never enough people b)
    people works on what they like.... May be someone like you
    can inspire & put together a team to make freebsd the best
    damn storage OS in the world! Actually what would be really
    neat is to factor out all FS code across all *BSDs so that
    rather than fixing the same old bugs N times, people work on
    different FS designs.

    The reality is that open OSes are still nowhere near what SGI
    boxes of a few years ago could do. I have heard of some NAS
    box vendors achieving really good performance but that
    doesn't help us in the open OS community (not to mention
    their advances will be lost when the company dies or is
    garbage collected by the likes of EMC, netApp).
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  • Next message: Steven Hartland: "Re: Very low disk performance on 5.x"