Vdbench and Data Validation against very large luns or files

One warning, something that some people have run into without knowing it:
If your luns are very large and your xfersize relatively small and your iops relatively small, then it may take quite a while before a data block is accessed for the second time, and therefore being read and its data validated.

For instance, with a one TB lun using an xfersize of 8k at 100 iops it will take 37282 hours or almost 5 years before each block is accessed ONCE.
You can make the lun look smaller by using the size= parameter
sd=sd1,lun=/dev/rdsk/cxtxdxsx,size=5g    (Vdbench then only uses the first 5gb of the lun)

or you can use the 'range= parameter:

sd=sd1,lun=/dev/rdsk/cxtxdxsx,range=(50,60) (Vdbench now only uses the space between the 50 and 60 percentile of the lun's size)



Henk.


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Blog for Henk Vandenbergh, author of Vdbench, and Sun StorageTek Workload Analysis Tool (Swat). This blog is used to keep you up to date about anything revolving around Swat and Vdbench.

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