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…
View original post 255 more words