RAID-5 was long hailed as the enterprise-level storage solution and a fit for nearly every application. The truth is, RAID-5 was designed back in the 80’s to save cost without completely sacrificing redundancy. Back then the cost per byte for storage on enterprise-class drives was so expensive that researchers were scrambling for a solution to store more data for less money.
Let’s say you needed 100MB of storage space and disk-level redundancy. Let’s also say, a 20MB SCSI drive cost $1,000.00. Before RAID-5, you’d buy 10 drives, create 5 RAID-1 arrays at 20MB each, and split your data set up to fit across these 5 separate arrays. Not only is this expensive at $10,000.00, but the storage space you require is split across 5 arrays. With RAID-5, 6 20MB disks gave you 100MB of space, and redundancy. That saves $4,000.00 per storage unit implemented! Sure, there were caveats, but with those kinds of savings, nobody was paying attention.
Welcome to the 21st century. The database is king, and everyone wants performance! Unfortunately, one of RAID-5’s biggest caveats is sacrificing performance, and developers and admins are finally starting to notice. Let’s take a look at the 5 biggest caveats of the RAID level most synonymous with enterprise storage for so many years:
- Performance, Performance, Performance! RAID-5 has significant write penalties all the time due to the requirement for parity calculation. Most implementations also suffer poor read performance, even though RAID-5 proponents consider this one of the “strengths” of RAID-5.
- Rebuild times are horrifying slow. Try days instead of hours for large storage arrays due to the need to read, calculate parity and write every disk in the array for each megabyte rebuilt. This can literally translate to days of downtime for a single disk failure depending on the I/O performance required for the storage to be usable.
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