Very inconsistent (read) speed on UFS2

[Daniel Kalchev]

On 31.08.11 14:37, Lev Serebryakov wrote:
>
>> If 5 simultaneously dds reading from the drives is very fast (way faster
>> than the above) and there aren't sporadic drops in performance which
>> aren't caused by writes (hence my "stop using the filesystem" comment),
>> then I think we've narrowed down where the issue lies -- not the drives.
>     Yep. It seems to be exactly like this.
>
This test does not rule out drive IOPS limits. Or drive cache trashing.

If you tell the drive to continuously read, or write mots of these IOs 
is served from/to drive cache, thus such large number of IOPS. More that 
the drive could handle if it has to move heads.

Not saying this is the case, but things may be as simple as filling up 
the write cache and the drive deciding to flush it out to platters, thus 
reducing read rate. These are desktop drives, apparently designed for 
non-threaded applications. "raw" read/write speeds may be high, but 
higher-performing drives at much higher price points offer much more 
performance, even at lower "raw" read/write rates. Just spending more 
for smarter controller.

Eliminate the writes and the drives might be worth their salt.

Daniel