Question

I have seen advice to ‘warm up’ EC2 to overcome a first write penalty:-

Warm up data partitions – There is one
drawback to using disk IO in EC2: a
“first write” performance hit when
initially writing to new partitions.
To avoid this penalty, you can “warm
up” the partition by executing a sort
of throw-away command that accesses
it. For example, you can use the Linux
dd command to write to the disk. While
the penalty still occurs and cannot be
avoided, at least the first write to
your databases will not suffer the
effects.

Source: http://answers.oreilly.com/topic/1345-getting-the-most-out-of-mysql-in-the-amazon-cloud/

…but I haven’t found any further advice on best practice! Is this true of EBS storage? Can anyone recommend the ‘dd’ syntax that will perform this warmup and how to ensure that all blocks are ‘warmed’?

Answer 1

Thanks for the pointer to AWS forum. I did post the question there after posting here, and received a response from Jason@AWS. The thread is here:-

http://developer.amazonwebservices.com/connect/message.jspa?messageID=198413#198413

…and his response was:-

There is a first- read penalty for
EBS volumes created from snapshots, as
the volume is made available before
all of the blocks have been
successfully loaded. You can negate
this penalty by forcing every block on
the volume to be read:

$ dd if=/dev/<device> of=/dev/null