Last month, Scott pointed out the really bad performance characteristics of the Dell PERC6 in RAID0 sequential write, particularly compared with RAID-5. Granted, this is not necessarily a red flag because few people use RAID 0 in production. Still, if one can't write code or test correctly, one should not be in the hardware/firmware business. Dell ...

Everytime a good product comes out, people seem to contrive bad ideas for what can be replaced, usually brains, or people with brains, or that people lacking brains can accomplish something on their own. Let me put it simply. Suppose one had a query that uses a nonclustered index, and required a key lookup, and the key lookup required a disk ...

An observant person has probably noticed that SQL queries requiring disk reads not only have longer duration but also higher CPU times. It is not hard then to deduce that disk access (for both HDD and SSD), which involves the OS performing an IO call, the SQL Server process finding a place in the buffer cache for the data pages, and possibly ...

I was just about ready to unleash a long accumulating stream of rants against SAN vendors for pushing seriously obsolete computers as powerful storage systems. Of course, in a final check of products specs, I saw that EMC just announced the new Clariion CX4 line. The previous CX3 line was built around the Intel E7520 chipset, which was a ...

In the next series of posts, I'll focus on SQL Server I/O, revisiting some common issues and taking a closer look at some others. In each post and as always, I'll make the case with specific data points from my tests. For the first two posts in this series, let me check out the read-ahead technique used by SQL server. Read-ahead is an important ...

In my previous post, I looked at how a typical OLTP workload may be affected by various controller cache configurations. And the conclusion was that giving too much cache (say all 512MB) to reads hurt the OLTP performance. The primary reason was that the writes from the OLTP workloads were starved of cache. Now, let's take a look at how the ...

In my previous post on the performance impact of controller cache configurations, I presented some empirical results showing the performance impact of configuring the controller cache to various read/write settings on large sequential I/Os.   Why did I single out large sequential I/Os? That's because large sequential I/Os are heavily used ...

In the next several blog posts, I’ll share with you some empirical results concerning the performance impact of configuring the read/write cache of a disk controller.   In the comments on Joe Chang’s blog at this site on Storage Performance for SQL Server, some statements were made concerning the performance impact of read cache in a disk ...

There is a perplexing lack of material on overall storage performance strategy for database servers. Too much of the content is narrowly focused on tuning techniques to improve performance over an unknown base. First, storage system IO performance is well understood from the science and engineering perspective. Second there is sufficient ...

Andrew Kelly in a recent post here advised visiting/revisiting the SQL Server I/O basics, and I completely agree. A firm grasp of the basics can make it easy to understand some system behaviors that otherwise may be puzzling at times. A question that is often asked is how SQL Server performs the I/O writes in its checkpoints. ...