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"IO Sizes and Alignments with DTrace" A Better Way than Using iostat Using DTrace to secure a more comprehensive view of IO sizes and alignments than is possible with iostat, for example, is the subject of Lisa Noordergraaf's blog IO Sizes and Alignments with DTrace. The problem with iostat, she writes, is that while the utility does show the total number of reads and writes, it does not provide the necessary detail about individual sizes and alignments (start addresses) of the IOs as DTrace can. Noordergraaf includes what she terms an "unsupported, evolving script" used internally at Sun that she declares is nevertheless a fairly useful bit of code and worth sharing. She writes that the script instruments a function in the sd driver, from where it histograms the sizes of IO packets. She also recommends using the product id string rather than major/minor device numbers to restrict information gathering to only those devices of interest, crediting Paul Riethmuller with this discovery. The blog presents code for the script, which she claims can track the number of total IOs issued for all devices while keeping detailed statistics only for those devices that have a product ID, in the case of the illustration, starting with "MARVEL." Noordergraaf notes further that the script produces limited output at five second intervals and prints the full histogram of IO sizes only when given a particular command that can be changed as one wishes. More Information
IO Sizes and Alignments with DTrace - Noordergraaf's blog entry
Link to the full align.d script
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Tracking IO sizes and alignments with DTrace
"IO Sizes and Alignments with DTrace"
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