Diagnosing slow disk write performance

Mike Lovell mike at dev-zero.net
Thu Feb 27 18:11:04 MST 2014

Hey everyone,
I have a co-worker that just got a new system and is having some trouble 
with the write performance of both of the drives in his system. One is a 
large hard drive and one is a SSD. On both drives he can read sequential 
data at over 100MB/sec. The write performance is horrible though. Both 
drives are only able to do sequential write at about 1.3MB/sec. I have 
checked the data alignment and both drives have partitions and 
filesystems aligned at 4K boundaries. He is running Ubuntu 12.04 with a 
3.11 kernel. The hardware is a ASRock z77 motherboard that has Intel and 
Asmedia SATA controllers. Changing which controller the drive is 
connected to doesn't help nor does changing whether it is the 3Gbps or 
6Gbps ports. The controllers are in AHCI mode. I don't remember what 
filesystem he is using but I'm guessing it is ext4 since that is the 
default in Ubuntu. There aren't any errors from the kernel and the SMART 
data says both drives are healthy. Do any of you have any suggestions as 
to things that might be causing this? Or things that could be tried to 
fix this?


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