I wanted to copy a file (40 gig dataset) from a single drive to a dual disk raid-0 drive. I tried with CP and it sustained read - 4mb and write - 11 mb (doesn't make sense I know (must be the stripe size), so lets just consider the bandwidth to be 4Mb) (monitored via iostat). My colleague suggested I use dd and send the USR1 signal to monitor the bandwidth.
DD starts off fine with a 40-50mb sustained read performance, however over time it has come down to 12.6mb/s (12 gig copied) -- edit degraded to 7 mb/s . I should be maintaining 40Mb/sec.
What strategies are there to enable sustaining maximum bandwidth potential ?
I am using arch 64 bit, the raid is software and has a stripe size of 128, all of the drives are a year or so old , western digitals (8 -16 mb cache), the machine I am using has 16 gigs of ram. Source filesystem is btrf and destination is ext4. My motherboard has 6 or so sata ports disk 1(source) is in port 3 and disk 2-3 from the raid are in 0 and 6 respectively·