Ask the Expert 2 - Storage Technology Magazine
Q: What are the variables to consider when determining how many host bus adapters (HBAs) are required per server?

A: The basic rule of thumb for how many HBAs to use is two for disk and one for tape. Using 2Gb Fibre Channel across two fabrics and two 2Gb storage ports, you should be able to stream data at over 300MB/s. If you're worried about IOPS, then two connections should be fine for most data intensive applications.

The only time I have needed to use more than two adapters on a particular server is in massive digital media environments and with humongous data warehouses.

If the server itself is involved in pushing data to tape, I always specify another adapter for tape streams. If not, and you're using serverless backup through the SAN, then two adapters should be fine. Each adapter should be able to handle between 128 and 256 LUN numbers, depending on the SAN environment. If you're connecting a Windows host, you will run out of drive letters long before you run out of LUNS.

--Christopher Poelker, storage architect, Hitachi Data Systems

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2003:		 What kinds of tools can help me find files that are no longer used?
Nov 2003: Can you please explain what content-addressed storage (CAS) is, and what it's used for?
Oct 2003: What do you think of serverless backup?
Sep 2003: How do NAS blades in director-class switches work? Will they become popular?
Aug 2003: Which is best for consolidating storage in an SAP environment: SAN or NAS?
Jul 2003: I have 60% free space on 10,000 PCs. Can I consolidate it by mounting it as a volume and using a login script to map it to the desktops?
Jun 2003: Can you describe the steps that a single byte takes when going from memory to a spinning spindle and back again?
May 2003: What trends do you see in open-systems backup and recovery environments?
Apr 2003: What tools can we use to replicate domestic and overseas databases to one another?
Mar 2003: We're building an HSM solution to which we'll write 100GB+/month and store it for seven years. Do you think we should use CD, DVD or tape?
Feb 2003: I want to consolidate 10TB+ of files onto one system. Would you recommend products from EMC, NetApp or one based on Microsoft's SAK?
Jan 2003: I'm out of disk space on my Sun server running Oracle. Is NAS a good choice?
Dec 2002: File server cluster vs. network load balanced vs. DFS: What's the best method for file server HA?
Nov 2002: What are the pros and cons of storing user files on a RAID array with either ATA or SCSI drives?
Oct 2002: Can you do a LAN-free data transfer by giving an IP address to a FC adapter? Does it decrease the speed of data transfers to LAN speeds?
Sep 2002: What is the average amount of hosts for a centralized system to backup at one time?
Aug 2002: Why doesn't my mail client software create a lock for e-mail files if it's reading it off a NAS device?
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July 2002: What does storage pooling mean? What do you think of it?
May 2002: What is the difference between a NAS gateway and a SAN appliance?
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Apr 2002: In terms of feed speed, what does that measurement refer to? Is it from the primary storage to the secondary storage? Does it stop at the write speed on the tape drive?
Mar 2002: How can you use solid-state disk (SSD) to accelerate SAN performance?

This was first published in January 2004