Troubleshooting your NAS system
By Christopher Poelker
Network attached storage (NAS) is used for host file services over an IP network. NAS is different from SAN in that NAS uses the CIFS or NFS protocol over IP, and SAN uses SCSI over FC. Since NAS relies on the reliability of IP network services, common network issues may affect NAS performance, connectivity and reliability.
NAS products come in various flavors, and can be implemented in a number of ways depending on the clients being served. The NFS protocol is native to Unix servers and clients, and the CIFS protocol is native to Windows servers and clients. You can present a NAS share by using standard servers using the native protocol, or use a NAS appliance that is configured to serve both Unix and Windows clients by running both protocols simultaneously. The use of NAS appliances has become more popular since they are tuned to provide a single task, which is serving files. Whichever approach you use, there are some common best practices which can be used with any platform.
Common issues that affect NAS products are:
- Software versions
- Network hardware
- Network connectivity
- NAS hardware
Converting from servers to a NAS appliance
Some appliances allow you to create virtual servers for representing NAS shares. Using virtual servers simplifies the migration to a NAS appliance, since each virtual server can mimic the same node name and IP address of the server it is replacing. If you are using a Linux-based appliance for Windows CIFS shares, make sure your appliance conforms to the latest Samba version -- Samba 2.0.21c. Also, make sure your clients are standardized with the latest patches and service packs applied to reduce version issues.
Use the right network
NAS performance can be an issue when supporting many clients at the same time. It is imperative to use the right network. When choosing network hardware for NAS, be sure it supports Virtual LANs (VLAN) for traffic isolation, and IP trunking or port channeling for bandwidth aggregation. Gigabit Ethernet is the best platform for NAS shares, as it provides the most robust bandwidth. Use "jumbo frames" when possible to increase performance for large file transfers, and configure your network for "full duplex" operation.
Your NAS product should be connected to at least two IP switches, and the product should be configured as a cluster so that either a switch failure or NAS head failure does not affect client connectivity. Popular appliances can take advantage of "virtual interfaces" that allow almost transparent failover to another IP port if one port or path goes down.
The underlying disks used for your NAS storage can dramatically affect performance. You should use hardware-based RAID protected storage for best availability and performance, since software-based RAID can cause performance issues during disk failures. Also, make sure you spread your network cards across PCI busses within the server to prevent internal bottlenecks.
Optical networks are more secure than copper networks, since the cables are more difficult to tap. The backbone of the NAS infrastructure should use optical connections. When implementing a security model for files over NAS that will be shared between Unix and Windows clients, make sure your NAS server can apply Unix-style security and can also be integrated with Windows ACL security and Active Directory.
When implementing NAS, using best practices can assure your infrastructure is reliable and can perform to meet the demands of your clients.
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About the author: Christopher Poelker is the co-author of SAN for Dummies.
13 Mar 2006
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