Mon, 03 Jul 2006
New hardware in Odysseus
After several months of having new disks and controller at my desk, I have
finally managed to install them to Odysseus.
Now Odysseus (ftp.linux.cz, ftp.cstug.cz, etc.) has
a shiny new SATA-2 PCI-X
controller (3ware 9550SX-8LP) with eight new 500 GB drives, almost doubling
its previous storage capacity.
It seems the new controller (with NCQ and bigger cache memory) is
according to iostat(8) able to keep all the drives busy
at 100% sustained when the demand is high enough. The previous one
- 3ware 7508 - was apparently not able to distribute the load equally:
when the load was high, the drives on which the
busiest volume (/var) was, were at 100%, while the others peaked
at about 75-80%.
I even had to upgrade my MRTG configuration, raising the maximum theoretical bandwidth of each drive. It seems the new drives have noticably higher throughput. However, it feels like the latency of the drives has increased during the load peaks. I am not sure what is the cause (maybe it is simply a throughput-for-latency tradeoff because of bigger caches everywhere). From the graphs it seems that the imbalanced HDD utilization problem is gone (altough it might have been a problem of a particular HDD firmware).
Another thing to note is, that SATA cables require bigger space behind the drive, because the SATA connector is almost a centimeter deeper than PATA one. I think I have cracked the connector in one drive while trying to fit the cable between the drive and the fan behind it (but the drive fortunately works).
When upgrading the system, I screwed up when moving the data to the new host: I ran the following command on the upgraded system, which has still been running on a temporary IP address:
rsync -aHSvx -e ssh --delete odysseus:/export/ /export/ && echo "OK"|mail -s rsync kas
Which used the address 127.0.0.1 for odysseus
(which was in /etc/hosts, because Anaconda sets it up this way).
So the above command on a temporary host actually did not do anything,
as it tried to synchronize the /export volume from itself. You
can laugh at me now. Oh well.