RAID-0 vs iSCSI vs HDD

I had reason to set up some storage at the office recently. So, I got to experiment with regular HDD storage, iSCSI and RAID-0 configurations. The results proved to be rather interesting and will be useful for future reference.

The same machine was configured with a two-disk RAID-0 array, the single HDD storage, and as a iSCSI initiator. The iSCSI target was connected via a 1Gbps network over CAT-5e via a gigabit switch. The iSCSI target had to be configured with TCP window scaling disabled in order to achieve a high speed connection.

All results are obtained with regular bonniee++ benchmarking tool.


Version 1.97 ------Sequential Output------ --Sequential Input- --Random-
Concurrency 1 -Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- --Seeks--
Machine Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP /sec %CP
XXX 8G 973 97 115588 9 49174 4 4013 65 118067 5 259.3 3
Latency 9549us 778ms 1391ms 113ms 321ms 763ms


Version 1.97 ------Sequential Output------ --Sequential Input- --Random-
Concurrency 1 -Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- --Seeks--
Machine Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP /sec %CP
XXX 8G 1247 97 272885 14 122170 6 4006 96 333448 8 341.0 10
Latency 9564us 25945us 217ms 7244us 34189us 376ms


Version 1.97 ------Sequential Output------ --Sequential Input- --Random-
Concurrency 1 -Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- --Seeks--
Machine Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP /sec %CP
XXX 8G 666 95 36609 3 24401 2 4598 96 90542 4 191.8 2
Latency 15935us 6439ms 4285ms 18451us 302ms 2075ms

There are some useful observations from this. The RAID-0 array has a higher read and write speed than any of the rest for both sequential and random access patterns. While the iSCSI device has the slowest read and write speed, its access speeds are still fairly acceptable. However, it has a significantly higher latency than the rest which makes it unsuitable for regular usage.

I’ve decided to configure the RAID-0 array for storage that requires high speed access as it has both high read/write speeds and low latency. The iSCSI storage is used only as backup storage, which is useful since it can be used to backup data across a network to a dedicated storage server. The regular HDD is used for regular OS storage.


SimpleSAMLphp with WordPress on OpenShift

These are the steps that I used to get SimpleSAMLphp running with WordPress on OpenShift.

First, copy the files up to the server and decompress them.

$ rhc scp MYAPP upload simplesamlphp.tar.gz app-root/data
$ rhc ssh MYAPP
$ cd app-root/data
$ tar -zxf simplesamlphp.tar.gz

Then, link it to a public WordPress directory e.g. uploads

$ cd uploads
$ ln -s ../simplesamlphp/www/ saml
$ cd ../simplesamlphp

Then, just configure SimpleSAMLphp as usual.

The only key thing to note is that the baseurlpath needs to be configured with a FULL path name. For some reason, SimpleSAMLphp was unable to detect that it was running behind a reverse proxy.

Ubuntu 12.04 LTS with Missing Dota2 Textures

There is a pretty well known bug with Dota2 under Linux on Intel graphics hardware. Essentially, models textures are missing as can be seen from the screenshot below:

I had at first tried installing lts-raring hardware enablement but that did not solve the problem and created new ones with my hardware. According to the bug-report, the problem was solved in Mesa 9.1.5 but lts-raring came with 9.1.4 only.

So, I downgraded back to lts-quantal and looked for another solution.

In the end, all I had to do was to add a 3rd party PPA to solve the problem:

# apt-add-repository ppa:glasen/intel-driver
# apt-get update
# apt-get -y dist-upgrade

This would install the Mesa 9.1.6 and Intel drivers, which solved the problem.

Now, I get to experience Dota2 in all its glory!

Quantal to Raring Upgrade

I faced the same Quantal to Raring upgrade problem on Ubuntu 12.04 LTS with Hardware Enablement as reported here.

In order to get it to work, I had to remove Xorg for Quantal then upgrade everything to Raring. I did this from the command line terminal:

$ service lightdm stop
$ apt-get autoremove xserver-xorg-lts-quantal
$ apt-get --install-recommends install linux-generic-lts-raring xserver-xorg-lts-raring libgl1-mesa-glx-lts-raring
$ apt-get install linux-tools-lts-raring

That was it. Upgraded to LTS-Raring hardware enablement kernel and Xorg.

PS: The only issue with this upgrade was that I lost back-light control on my XPS13 laptop as reported here.

RTL8192CU Issues

The TL-WN725N nano dongle is a cheap way to get 802.11n wireless connections up. However, the RTL8192CU chipset has issues under Linux.

After a whole day of trouble-shooting and digging, the best solution that I came to is this: use the driver supplied by Realtek!

First, the built-in kernel driver rtl8192cu needs to be disabled.

$ echo "blacklist rtl8192cu" >> /etc/modprobe.d/rtl8192cu.conf

Next, download, unzip and build the Realtek driver. Just run the included script.

$ bash

That’s it! All other configurations as per usual.

HP ML110 G7 Fan Noise

I love the fact that HP sells servers retail in Malaysia. It’s so convenient to just pick one up from the local store instead of going through all the procedures of issuing a PO etc.

However, the ML110 G7 that I picked up a couple of weeks ago, has one rather major problem – its fans run at full speed all the time.

Granted, the server room in the office is not air-conditioned but I keep the windows open for natural ventilation. The temperature itself is just normal room temperature, as confirmed by the air-intake sensors of the server.

Although the server is the main work-horse of the entire office, it’s a small office and the work-load isn’t heavy. Most of the time, the load average is only at about 11% with the CPU clocked down to the slowest possible speed.

So, it was a pain to find that the three fans were running at a 100%:84%:10% ratio all the time. There’s no real reason to do this since the temperatures are all within a very reasonable range.

Now this wouldn’t be too much of a problem except that the fans running at those speeds sound like a jet plane taking off. It’s a small office and the noise is noticeable above the air-conditioner’s even though it sits in its own room.

It took me a little bit of sleuthing and experimenting but the final trick that did it was to simply upgrade both the BIOS (10-Aug-2012) and ILO (1.50) firmware to the latest versions.

Now, the fans only hover at a very reasonable 78%:66%:11% ratio on a very hot afternoon.