Very good post.
Out there in IBM land the field technical and sales people are often given a guideline of between 5% and 10% of total NAS capacity being allocated for metadata on SONAS or Storwize V7000 Unified systems. I instinctively knew that 10% was too high, but like an obedient little cog in the machine I have been dutifully deducting 5% from the estimated nett capacity that I have sized for customers – but no more!
Being able to size metadata more accurately becomes especially important when a customer wants to place the metadata on SSDs so as to speed up file creation/deletion but more particularly inode scans associated with replication or anti-virus.
[updated slightly on 130721]
The theory of gpfs metadata sizing is explained here and the really short version is that in most cases you will be OK with allowing 1 KiB per file per copy of metadata, but the…
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IBM Redbooks (@IBMRedbooks) tweeted at 9:15 PM on Fri, Jan 18, 2013:
Learn about Configuring SDDPCM for High Availability in our #IBMRedbooks Redpaper here: http://t.co/iO34fEYu
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If no IO (input/output) operation is the best IO, than the second best IO is the one that can be done as close to the application and processor with best locality of reference. Then the third best IO is the one that can be done in less time, or at least cost or impact to the requesting application which means moving further down the memory and storage stack.
IBM Storage Taneja Group analyst report: Reduce costs with SVC and IBM Real-time Compression http://t.co/sv34Dvv6 (https://twitter.com/IBMStorage/status/289872861466865664)