Storage consolidation trade-offs

Buyer beware! It's an old adage but a relevant one. I recently had an e-mail from a customer who complained to me about companies that sell network-attached storage appliances with data protection via RAID (redundant arrays of independent/inexpensive disk). His complaint was that these NAS vendors mislead their customers and fail to provide adequate support when disk failures occur.

This particular customer wanted to consolidate his company's file-serving requirements to one system. While the user's capacity requirement was not huge, the company was concerned about having all that data in one place without some form of protection. A NAS solution seemed to meet its requirements.

Due to financial constraints, a low-end solution from a reseller was chosen. The solution claimed to support RAID protection, alleviating the user's concern for the data.

When the NAS appliance arrived, the user configured the storage associated with the solution. There were two hard disk drives attached to the NAS head. These drives arrived configured with RAID 1. This RAID level that is commonly called "mirroring" and delivers simple data redundancy by copying the data to each of the disks. Theoretically, if one disk fails, applications can access the data on the other disk.

The only other RAID level supported with this NAS appliance was level 0 (zero). This RAID level delivers the greatest performance because the data is broken into smaller segments, which are then written onto the all the disks involved (two in this case). This means when reading or writing the data, all the disks are working on the same dataset rather than just one, producing greater throughput. However, simply striping data provides no protection for the data, only performance.

This customer, following the vendor directions, configured the disks to meet their protection requirements. And everything was good... for a while. Then one of the disks failed. This is where the problems began.

When the disk failed, the NAS appliance failed. The customer was not able to access ANY of their data from either disk.

Like reasonable people, they went to the instruction manual to see if there was something else they were supposed to do to fail-over to the other, mirrored disk. Obviously, the fail-over was not automatic because they couldn't access the data.

What they found was, there were no instructions on what to do in the event of a disk failure when RAID 1 had been configured.

Like many customers, the talk of easing management pain by consolidating file storage with RAID protection, appealed to these people. When they found a solution that matched both their application and budgetary requirements they implemented it. What they learned was not all solutions are created equal.

These customers are now frustrated because the solution they thought they had failed them, possibly over the lack of adequate documentation.

In this customer's story, the failure happened to be with a NAS appliance. This same failure can happen with any RAID array configured at level 0 (or 1). So, the moral of this story is, especially when consolidating files to one storage subsystem, whether it be NAS or a storage area network, understand the protection/cost trade-offs and make sure, when you open the box, all the documentation is present.

Anne Skamarock is an analyst with Enterprise Management Associates (http://www.enterprisemanagement.com). She has worked with networked storage for the last 15 years and is currently focused on the storage practice within EMA. She can be reached at askamarock@enterprisemanagement.com

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