Control Group Blog

As I’ve mentioned in previous posts about testing storage performance with lmdd and bonnie++, different applications require different characteristics from storage to provide the best performance. I’ve highlighted some tests that are good for large streaming files like video, and small file transactions like databases or mail servers. Today I want to look at a tool that runs a series of tests in many different ways to provide you with a holistic view of what the storage can and can’t do.

This tool is called iozone. iozone is open source and runs on a ton of operating systems (including Windows). It runs several tests which can take some time to complete but provide the best overall view of the capabilities of a piece of storage. For instance, iozone runs a write test with files of different sizes and with different size records (the amount of data written at a time). It does this over and over again with writes, reads, random writes, random reads, and so forth. Since it’s running all these tests you can see what sorts of operations will have good performance and which ones will not perform so well. Check out the iozone documentation here.

One really great thing about iozone is that the output it generates can be easily placed in a spreadsheet program like Excel to generate a great 3d diagram describing your storage. Here’s a diagram I generated from some tests on a Linux server.

Results of a write test with iozone

This particular server performed quite well with large files and a record size around 1 MB (interesting to note, this is the same storage from the lmdd post. Notice that the parameters I tested with there are the same as the best write that this disk can do according to iozone!).

If you’ve been following my posts on storage performance testing I hope you’ve learned about some new tools that you can use to see what’s going on. I use these on every deployment to make sure we’re giving our clients solutions that they can depend for performance and reliability. As always, let me know if you have any questions about these tools. Happy testing!

Last time I posted about checking disk performance with lmdd. lmdd is great for checking streaming throughput, but what if you have a different kind of application? Every application accesses storage in different ways: with video we need to be able to provide constant throughput when writing a lot of data to the disk, but other applications may have different storage needs. For example, a database can make lots of very small changes to the data on disk in a short period of time. The best performing disk for a database will probably need to have very low seek time and good transactional performance.

bonnie++ is a series of file system tests that focuses on small files. It was designed to behave like a mail server does, creating and dealing with lots of small files (emails). bonnie++ is easy to run and outputs a CSV file that you can view with something like Excel. With the bon_csv2html command you can quickly generate html pages from the CSVs.

Here’s the output from bonnie++ running on a server:

The HTML output of bonnie++ on a Linux Server

At first glance the output can seem quite cryptic, but if we look close we can see that this provides us a great amount of information about latency and speed on different filesystem operations. I generally run this several times as I make changes to verify that the storage is providing the right performance characteristics. Tweaking a file system to make file system operations happen a few milliseconds faster may seem ridiculous, but in some environments it can make a huge difference.

Next time I’ll post about a tool that’s new to me but can test a disk in so many different ways I’m planning to run it on every system we install from now on.

One of the unique things about how Control Group works is that our focus is much more involved than simply putting in a solution for a client and then moving on. We work with our clients to determine how they work, so we can design IT solutions that really fit their needs. Since we have partnerships with a variety of vendors, we work with our clients to arrive at the best solutions for their business. This means we do quite a bit of research and planning before we begin a project — and then a great deal of testing during and after we install new hardware or software.

I do some work on implementing storage systems for our clients, and we’ve found that different applications have different storage requirements. For example a video post production facility — like the facility at WWE — generally needs lots of disk space that is very good at reading and writing large files at high speeds. The storage here needs to provide good streaming throughput, because high quality video files generally have high bit rates, and are being stored or played back from the disk in real-time for ingesting, editing, or playout. If the storage system is not fast enough to read or write the file in real-time, frames will be dropped. This can cause unsatisfactory media files, programs to crash, or audio and video to become out of sync.

10,000 RPM SAS disks. That's some serious storage.

Suboptimal read/write performance can become a huge problem. When we put in a new system this is something we need to test. I usually do the test with a tool called lmdd.

lmdd comes from the lmbench tools which are provided by Bitmover for benchmarking systems. lmdd is great for testing streaming bandwidth. In most of our engagements with video, we install a Stornext or Xsan filesystem so we’ll run our tests against this. lmdd will probably work on any filesystem that you can mount on your Mac or Linux computer (Leave a comment if you need a version for Mac OS X, I have one compiled).  lmdd lets us verify exactly what the maximum number of megabytes per second we can push through the storage and point us to where we need to make changes to the hardware or software configuration. I use lmdd like this :

lmdd of=/path/to/test_file count=1g

lmdd if=/path/to/test_file

The first tests write performance and the second tests read performance. More information about the syntax is available in the manual page for lmdd. The results of the command from a server I was testing looked like this:

2147.4755 MB in 6.8003 secs, 315.7914 MB/sec

lmdd is great because it’s easy to read. This result shows I could write to the filesystem at 315 megabytes per second. That’s really fast! This is from a test with a server with a lot of RAM and a special filesystem that took advantage of that cache. When I run it on my Macbook, I get a result like this:

18342.6171 MB in 376.7685 secs, 48.6841 MB/sec

So the next time you’re interested in how your storage is performing give lmdd a shot and let me know how it goes. If you’re looking for more information about storage performance testing then stay tuned; I’ll be posting about testing storage with tools that benchmark small reads and writes next.

I was recently having a conversation with a friend and we both laughed when we thought back to the first five hundred megabyte hard drives that we had owned. Back then, the half-gigabyte drive was ridiculously expensive and physically huge. We both thought that it would be impossible to fill these drives up.

This of course was not the case. Now you’re lucky if an application can be installed in less than 500 MB, and as hard disk sizes grow, we find new ways to fill them up with applications, documents, and media. Digital files have become the most valued assets for most of our customers, so the organization, storage, and archiving of data is a serious concern.

I find that the best way to evaluate storage technologies solutions for our clients is to step back and take a look at the problems the client is looking to solve and the priorities dictated by their business needs. Usually, our clients’ storage needs require a combination of performance, reliability, disaster recovery, scalability, and manageability. Fortunately technology has stepped up to the challenge to handle the increased need for larger, faster, and more reliable storage.

Storage networking is a general term that encompasses many different technologies that provide excellent solutions to modern storage problems. A storage area network (SAN) is an architecture in which storage devices are connected in a high-speed, dedicated network and are presented to computers that are part of the same network. Using storage networking, we can accommodate our clients’ performance and reliability needs: by abstracting groups of hard drives as logical units (LUNs) we can stripe data across disks to increase speed and add redundancy by storing parity on the disks. This configuration will allow us to rebuild the LUN when a disk fails, without causing downtime or data loss.

Example SAN Configuration for Final Cut Pro Editing

A storage network abstracts the underlying hardware that provides storage services, providing some great advantages for disaster recovery. When we add tape libraries to a SAN we can make backups quickly and efficiently without slowing down the network or computers on it. We can also connect a SAN to another SAN that’s in a different building or even a different state. This allows us to easily replicate data to a secondary location so our clients can be up and running quickly if there is some kind of catastrophe in the data center.

Even the largest SANs will eventually get filled up with data. What happens when it’s time to increase capacity? With traditional storage, the system is shut down, new equipment is installed, and the data is migrated. This typically involves downtime and runs the risk of data loss if something goes wrong. With a SAN expansion is no problem. Since the storage services are abstracted from the storage hardware it’s easy to add capacity or replace older equipment, in many cases involving no downtime.

A SAN also provides centralized management for storage: administrators can look in one place to see the status of all storage in a data center.  This allows businesses to evaluate storage health and utilization, which can prevent problems and help plan for future growth.

As data becomes a more and more important part of business strategy, it becomes critical for businesses to have larger, faster, and more reliable storage services to keep things operating smoothly. Storage networking is a core component of these strategies. I’ll continue posting about our thoughts and experiences with SAN solutions, and try to shed some light on the storage ecosystem as new technologies emerge.