Server Storage - RAID, WHS, and Throughput

Feb 10 2009

The discussion, here, about larger storage setups caught my attention this week. Large storage setups for many simultaneous users have considerations beyond your standard small home server. Some of the major considerations are hard drive choice, disk configuration, sufficient throughput for your application, backup, fault tolerance.

- Hard Drives: If you are planning a large 10TB+ array of discs, you may want to consider enterprise class drives from leading hard drive manufacturers. These drives are certified for 24/7 operation, and warrantied for 5 years. However, there is a price for the higher reliability drives. Western Digital Enterprise Class Green Power drives cost about 80% more than their equivalent consumer version.

- Disk Configurations (from Wikipedia):


  • RAID 0 (striped disks) distributes data across several disks in a way that gives improved speed and full capacity, but all data on all disks will be lost if any one disk fails.
  • RAID 1 (mirrored settings/disks) could be described as a real-time backup solution. Two (or more) disks each store exactly the same data, at the same time, and at all times. Data is not lost as long as one disk survives. Total capacity of the array is simply the capacity of one disk. At any given instant, each disk in the array is simply identical to every other disk in the array. - IS BACKUP
  • RAID 5 (striped disks with parity) combines three or more disks in a way that protects data against loss of any one disk; the storage capacity of the array is reduced by one disk. - NOT BACKUP
  • RAID 6 (striped disks with dual parity) (less common) can recover from the loss of two disks. - NOT BACKUP
Windows Home Server Drive Extender - a file-based replication system that provides three key capabilities:
  • Multi-disk redundancy so that if any given disk fails, data is not lost - NOT BACKUP
  • Folder Duplication - allowing the selective backup of any of your shared folders, keeps duplicate copies of specified folders on seperate drives, must manually enable - IS BACKUP
  • Arbitrary storage expansion by supporting any type of hard disk drive (Serial ATA, USB, FireWire etc.) in any mixture and capacity — similar in concept to JBOD
  • A single folder namespace (no drive letters)

- Transfer Rates

The throughput of the system may or may not be important to you. You'll want to check on the specific card you plan on purchasing. Real world transfer rates can be very different from what is advertised on the box. The hardware raid cards will be faster and are capable of supporting many users. The hardware solutions can easily handle throughput from many drives simultaneously without degradation of performance. If the files accessed are on different drives, the total throughput can be quite high. WHS Drive Extender is a software solution and much more appropriate for a small number of users/simultaneous file transfers.

- Backup / Fault Tolerance

All of the above mentioned solutions for creating large storage arrays are really not good backup solution for critical data (except RAID 1). Many of them do have fault tolerance, allowing them to rebuild the array by replacing a broken drive. In the case of hardware RAID, the RAID card is also a fault point and would likely need to be replaced with the same model card to get the array back up and running. For critical backup you will need a separate solution. I have been considering this for my family photos. Movies and music are replaceable, while family photos aren't.

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