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DD command using block device as input
Post 302666057 by nytty on Tuesday 3rd of July 2012 03:27:08 PM
07-03-2012
Alright, I get your point. I though that using /dev/sdb1 moves to position 0 
AFAIK hdparm only gives you the speed of the disk and not the time of reading a given amount of data.
So far with my tests I find that reading 16kb takes about the same time as reading 512b. I need this information to set the optimal page size of my system (oracle and mysql suggest these sizes)
Can you elaborate on why dropping the caches is a bad idea?
How about this sudo procedure:
- drop_caches
- flush disk-cache with hdparm
- make sure dd is in memory
- position the read head randomly on disk
- with DD: read X amount of bytes from the beginning of my file (this is timed)
AFAIK hdparm only gives you the speed of the disk and not the time of reading a given amount of data.
So far with my tests I find that reading 16kb takes about the same time as reading 512b. I need this information to set the optimal page size of my system (oracle and mysql suggest these sizes)
Can you elaborate on why dropping the caches is a bad idea?
How about this sudo procedure:
- drop_caches
- flush disk-cache with hdparm
- make sure dd is in memory
- position the read head randomly on disk
- with DD: read X amount of bytes from the beginning of my file (this is timed)
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