Re: cloning to multiple drives with the "dd" command.

[Ray Dillinger]

On 02/23/2015 01:29 PM, Bob Proulx wrote:
> didier chavaroche wrote:
>> Ok, I recognize trying to clone 23 disks a once can be a little bit
>> hard for my system.
> 
> Yes.  To say the least!  That could be a very large amount of data.
> All divided by the total available bus bandwidth which will be around
> 100M/s.
> 

It sounds to me like the disk cache is mindlessly kicking out the oldest
data first; usually a good strategy for random-access
but has very bad behavior when dealing with large data
sequentially.  On sequential transfers it transitions from a
100% cache hit rate to a 100% cache miss rate when data gets
even 1kbyte larger than cache.

It is counterintuitive, but randomizing which sectors get kicked
out of cache leads to much more consistent behavior with sequential
access on data whose size approaches the size of cache and AFAIK
does not substantially degrade the cache hit ratio on random-access
data.

                                Bear

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