Inconsistent IO speed with dd command
Issue
- When I write to the disk and overwriting the file I get significant performance drop:
# time sh -c "dd if=/dev/zero of=ddfile bs=8k count=100000 ; sync"
100000+0 records in
100000+0 records out
819200000 bytes (819 MB) copied, 0.778416 s, 1.1 GB/s
real 0m9.528s
user 0m0.018s
sys 0m0.594s
# time sh -c "dd if=/dev/zero of=ddfile bs=8k count=100000 ; sync"
100000+0 records in
100000+0 records out
819200000 bytes (819 MB) copied, 7.76798 s, 105 MB/s
real 0m9.376s
user 0m0.011s
sys 0m1.084s
Environment
- Red Hat Enterprise Linux
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