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Using 4 or 5 8TB Hard Drives: Singly or RAID and How?
This page and the pages that follow discusses overall considerations for putting 4 or 5 high-capacity hard drives to use in the most appropriate way.
Questions? One-on-one consulting is available with Lloyd.
The pages that follow show various topologies, including single drives as single volumes, one large fault-tolerant volume, or multiple fault-tolerant volumes.
- TIP: use diglloydTools IntegrityChecker to verify backup integrity.
- RAID-4 is functionally equivalent to RAID-5 but may perform just slightly faster for reads. This terms are used interchangeably on this page.
- Capacity numbers have to do with TiB (1024^4) or TB (1000^4). Drives are designated using TB (1000^4), so an 8TB drive is 8,000,000,000,0000 bytes (8 * 1000^4) which makes it a 7.28 TiB drive.
- (!) Please review Drive vs Volume for the proper terminology used here.
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Four drives or five?
Some topologies discussed here require dual OWC Thunderbay 4 units, since one unit houses four drives, and there are five drives involved in some of the configs. The use of five 8TB drives instead of four drives for a RAID-4 or RAID-5 has benefits:
- Reduces the parity overhead to 20%, down from 25% for a 4-drive config.
- Increases performance substantially: 5 drives in RAID-4/RAID-5 is roughly the speed of a 4-drive RAID-0 stripe. With a 4-drive setup RAID-4/5 setup, the speed is roughly the speed of a 3-drive stripe. So the performance is about 1/3 faster just by using one more drive.
- Allows creation of three 10TB partitions from five 8TB drives (10TB is a forward-looking capacity for mid 2016, allowing for several years growth in capacity needs).
Approaches follow on subsequent pages.