[plug] Ubuntu woes

[Steve Baker]

Daniel Pittman wrote:
> Steve Baker <steve at iinet.net.au> writes:
>
>   
>> Nothing out of the ordinary in the kern.log, messages, syslog,
>> daemon.log, or the usual suspects in /var/log.
>>
>> All disks are in a hardware RAID - 8-port adaptec SATA-II raid card, 2
>> discs in RAID-1 and 6 in RAID-5.  The two RAID-1 drives are 12 months
>> or so old, the other 6 are all new.  My next plan is to find the
>> afatools kit from Adaptec and run the afacli command to check the
>> SMART status of the discs and then scrub (check) the arrays.
>>
>> What is confusing is some tasks are quite quick and others really
>> slow.  Unpacking a tgz archive was quick, aptitude safe-upgrade takes
>> a long time to do steps like read state information, build the tag
>> database, etc. but the download was quick, then it took even longer to
>> do the post-installation steps.
>>     
>
> It sounds, to me, very much like your system is delivering good write
> bandwidth[1] but terrible read bandwidth or latency.
>
> Unpacking the tar is fast iff the content is in memory, but the update
> is slow when it reads databases or faults in code from disk.  Network
> runs at full speed, and the post-install was slow only where it had to
> fault in code, etc...
>   
Sounds like a good theory - I am not sure of the best way to test this 
though.  I know of hdparm/sdparm but I don't know if they are 
appropriate for RAID volumes.  I can time large file copies and such (eg 
dd if=/dev/urandom of=/some/file bs=1048576 count=1024 or whatever) but 
I have nothing to compare results to.  And how do I stop caching from 
upsetting the results?
> At a guess.  Oh, are you running a vendor driver for the Adaptec card,
> or is it all open source drivers?
>   
I'm running the default Ubuntu aacraid driver.  When I ran the installer 
it found that driver automatically, so I just used that.  In my 
experience the aacraid drivers have been pretty stable and reliable, and 
I believe that Adaptec have always been quite open about providing specs 
for their hardware.  Of course it's a new-ish card (I don't have the 
model no. handy) so the driver may not support it properly yet, although 
I think that's unlikely.

Something I forgot to mention is that it's also very slow to boot, which 
could indicate a hardware level issue with the RAID card (or maybe it 
slows down after the kernel loads the raid driver).  I think it's the 
most recent firmware revision but I'll check on that too.

Regards,
Steve