Posts tagged ‘bandwidth’

April 9, 2011

3 simple steps to adopt cloud computing

Cloud computing is now synonymous with Flexible Provisioning and Scale. Find out below if you are taking full advantage of cloud computing.

The As Is deployment – lowest adoption cost, reasonable benefits:

Move the server application “as is” to a cloud server. This is nothing but a co-located server, at Amazon for example. The provisioning and maintenance of the application is still a self driven task.

The win is in the dynamic on demand provisioning. Easy to compute the ROI here. Let us say that your application needs to be available all year round – but cater to seasonal demands. Say it costs $400 to host your application to cater to peak demand. You would end up paying 12*400 = $4800 per annum to keep your application up. Most of the time it would be under utilized. Cloud computing has made it really simple to change your compute capacity as easily as setting a reminder in your out look calender. With amazon or google, you could just log into the admin panel and say that you need additional resources only on certain dates. At the end of the month you get billed for the amount of resources you actually consume.

The Managed RDBMS deployment – reasonably low adoption cost, reasonable benefits:

A lot of work has to be done to ensure that the application is available. i.e. a replication strategy and policy to keep the database available. This is still a lot of effort and money. The alternative is a managed RDBMS, where the provider (amazon or google) manages the database. They worry about keeping the data safe from being lost. Much harder to do the ROI here – as the time spent in managing this would have to be offset against opportunity costs. Note that there would be some amount of code restructuring (not a lot) to get this going. An example of this is the Amazon MySQL RDS. At the time of writing, google is yet to announce the availability of their hosted sql service.

The Application Rewrite – highest adoption cost, highest benefits (arguably)

If your goal is to write an application which scales very well then you should consider a complete application rewrite to take advantage of the storage APIs. Hosted RDBMS is still a single machine (or a cluster) running a database server – with bottlenecks – be it memory, cpu, networ or disk.

Cloud computing offers storage APIs to access and manage data unlike traditional methods of file or rdbms storage. Because of the underlying architectural differences, cloud datastore offers better scalability – http://labs.google.com/papers/bigtable.html.

April 8, 2011

Performance Engineering – SSD file systems.

Solid state device threatens to challenge and change existing computing paradigms.

While traditional disk access times are of the order of a few milli seconds, ssd access times are under 100 micro seconds for reads and writes respectively. Speeding up by a factor of 100. And that is significant.

Operating system components have evolved over the last 4 decades at a much slower speed. For an enterprise platform like IBM AIX or HPUX it takes A few years (my guess is a minimum 6) to push a new technology. The cycle is as follows – a new hardware technology is invented. OS vendors take a few years to adopt and evangelize. Enterprise customers longer to test, adopt and deploy.

SSD promises to deliver better performance by lowering IO latency and increasing throughput. File systems have evolved to do the same. Specialized caches have been invented to speed up performance. For example directory name lookup cache, page cache, inode cache, large directory cache, buffer cache and so on.

Quite a lot of focus is on being clever with reads and writes of application data. Engineers go to great extents to squeeze the last bit of performance out of the system. Sadly performance is not a main consideration during implementation (functionality is) and is often times applied as an afterthought.

The result is hacks rather than elegant solutions to performance issues.

Coming back to SSDs – a large portion of the file system implementation has to be re looked at and parts of it have to be thrown away completely. Especially true when complete filesystems are laid out on SSD. We need to look at how filesystems can take advantage of SSDs.

April 5, 2011

Performance Engineering: IO Latency Vs Bandwidth

It is important to understand if the performance problem is due to the latency or the bandwidth. These two are very different phenomena but they may have similar looking outcomes.
In case of latency a transaction or an IO is taking a long time to complete. The question would be: is the time taken to complete the transaction reasonable or is it longer than what is desired. In many cases, the latency is unavoidable but one can use several techniques such as filling the pipeline or sending the IO in blocks. And storing in the buffer to hide the delay due to latency.
Bandwidth on the other hand, sometimes the performance is low because either the bandwidth is not utilized fully or it is inadequate. Even in this case one would observe low performance. To improve the performance which is limited by bandwidth, one has to understand and match the bandwidth of various devices along the IO path.  Several techniques can be used to optimize the bandwidth. Such as load balancing, multi path and adaptively adjusting the parameters.