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Rich Freeman, mused, then expounded: |
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> On Fri, Jun 21, 2013 at 3:31 AM, Duncan <1i5t5.duncan@×××.net> wrote: |
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> |
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> > The single down side to raid1 as opposed to raid5/6 is the loss of the |
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> > extra space made available by the data striping, 3*single-device-space in |
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> > the case of 5-way raid6 (or 4-way raid5) vs. 1*single-device-space in the |
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> > case of raid1. Otherwise, no contest, hands down, raid1 over raid6. |
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> |
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> This is a HUGE downside. The only downside to raid1 over not having |
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> raid at all is that your disk space cost doubles. raid5/6 is |
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> considerably cheaper in that regard. In a 5-disk raid5 the cost of |
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> redundancy is only 25% more, vs a 100% additional cost for raid1. To |
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> accomplish the same space as a 5-disk raid5 you'd need 8 disks. Sure, |
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> read performance would be vastly superior, but if you're going to |
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> spend $300 more on hard drives and whatever it takes to get so many |
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> SATA ports on your system you could instead add an extra 32GB of RAM |
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> or put your OS on a mirrored SSD. I suspect that both of those |
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> options on a typical workload are going to make a far bigger |
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> improvement in performance. |
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> |
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|
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However, the incidence of failure is less with RAID1 than RAID5/6. As |
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the number of devices increases, the failure rate increases. Indeed, |
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the performance and total space can outweigh the increase in device |
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failure. However, more devices - especially more devices that have |
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motrs and bearings, takes more power, generates more heat, and increases |
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the need for more backups to avert an increase in failures. |
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|
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Bob |
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-- |
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