swapcache Setup

Matthew Dillon dillon at apollo.backplane.com
Mon May 24 20:15:26 PDT 2010

:On Mon, May 24, 2010 4:42 pm, Matthew Dillon wrote:
:>     For a manufacturer-fresh SSD configuring only 32G out of the 40G
:>     leaves 8G which the SSD firmware will use to enhance its wear-leveling
:>     algorithms, improving the overall life of the SSD.
:What's the wear rate you've seen on the machines with SSD that you set up?
: (assuming that the SSDs are still in there and you've been tracking
:overall I/O)  I recall that the wear rate was comfortingly low.

    I've been doing a running test for the last few months on pkgbox64
    using the 40G Intel MLC SSD.  The work load is the daily bulk build
    with the swapcache set to cache data & meta-data, plus normal paging
    activity from tmpfs operation.

    At the moment smartctl shows ~4TB worth of writes and the wear
    indicator is at 97%.  It started at 99% so presumably that's 2% wear
    so far.

    This gives us (so far) a run-rate of 2TB per 1%-wear which comes to a
    durability of around 200TB.  This is extremely good.

    Intel specs this particular SSD as having a durability of 35TB (which
    is what you get with a normal filesystem doing normal windows-like
    activities).  The theoretical best-case with MLC flash is a 400TB
    durability with a 40G device (10,000 erase cycles).

    It takes a month or two for the wear indicator to tick over at current
    load levels.  Every time it does I get a better feel for the actual
    durability.  So far I am very impressed with the Intel SSD.

					Matthew Dillon 
					<dillon at backplane.com>

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