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Linchi Shea

Checking out SQL Server via empirical data points

Database Physical Storage Design

In June 2006, Microsoft published a SQL Server technical paper on Physical Database Storage Design. This paper was updated in February 2007. The paper is generally well written, and the recommendations are reasonable.

However, the following two specific recommendations caught my attention:

  • For small servers with less than three disks performing mostly sequential I/O, or servers with approximately eight disks performing random I/O, PCI is sufficient. However, PCI-X is recommended and can service a wider range of servers with varying workload size.
  • Directly attached I/O is recommended for small- to medium-sized servers

These two recommendations strike me as a bit odd or dated.

The PCI-X recommendation. It appears to be recommending PCI-X for anything other than small servers.

The current trend in database servers (such as the HP ProLiant DL servers) is to emphasize PCI-Express, though PCI-X and PCI-Express will co-exist for a while. Take a look at a standard HP ProLiant DL585 G2. This server has seven PCI-Express slots with a total of 40 lanes, supporting up to a theoretical I/O throughput of 10GB/sec. The server also has two 100MHz/64bit PCI-X slots, supporting a max of 1.6GB/sec I/O throughput. Contrast DL585 G2 with its predecessor DL585 G1 which has eight PCI-X slots with no support for PCI-Express. Another server that supports both PCI-X and PCI-Express is Sun Fire X4600. Similar to DL585 G2, X4600 support two PCI-X slots and 40 PCI-Express lanes.

The paper does mention that, "PCI-E is now commonly found on newer desktops and might soon be more widely accepted on small servers." DL585 G2 and X4600 can hardly be called small servers, and note that DL585 G2 was introduced in 2006.

The Directly Attached I/O recommendation. This is a bit odd because server size is often not a critical factor in deciding whether to use directly attached storage. Considerations such disaster recovery, performance, and cost are often more important.

Well, a few months in the server and storage world can be a long time. That makes it tough to keep a paper of this nature up to date all the time. Nevertheless, since the paper appears to be widely read, it would help to keep it updated.

Published Monday, November 19, 2007 2:15 AM by Linchi Shea
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James Luetkehoelter said:

Great points on both accounts! Especially the one about locally attached storage - the business drivers usually determine whether locally attached storage is used.

November 19, 2007 11:17 AM
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Checking out SQL Server via empirical data points

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