Re: Uneven load on drives in ZFS RAIDZ1

Am 19.12.2011 22:00, schrieb Garrett Cooper:
> On Dec 19, 2011, at 12:54 PM, Stefan Esser wrote:
>> But it seems that others do not observe the asymmetric distribution of
>> requests, which makes me wonder whether I happen to have meta data
>> arranged in such a way that it is always read from ada0 or ada1, but not
>> (or rarely) from ada2 or ada3. That could explain it, including the fact
>> that raidz1 over other numbers of drives 8e.g. 3 or 6) apparently show a
>> much more symmetric distribution of read requests.
> 
> Basic question: does one set of drives vibrate differently than the other set?

No: All drives are mounted in similar cages in a midi tower case (and
since I did not like the temperature rising to 45C, last summer, I added
case fans to keep the temperature of all drives equally low, too).

But I'll try swapping drives (or rather SATA ports) tomorrow. If the
drives are different (hardware or data on the drives), then the higher
load will move, but if it's in the ZFS code, then I expect the higher
request rate to stay on the first two drives. I'll report the outcome.

(And repeating what I wrote before: The drives seem to behave perfectly
well, they do just receive different numbers of read requests although
the pool appears to be symmetric with regard to all factors that could
have an impact. I really doubt this is caused by hardware, else there
would be observable differences in latency or queue length.)

Regards, STefan