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
Subscriber exclusive content
A Red Hat subscription provides unlimited access to our knowledgebase, tools, and much more.