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| Registered: June 9, 2007 |  Posts: 1,208 |
| | Posted: | | | | I'm thinking of putting together a raid 5 array but I'm unsure of a few things.
I've heard that with raid 5 you have to use disks of the same size and type. Does this mean it has to be the exact same drive? If one of the drives go a few years down the line I don't want to be forced to buy all new drives because the same drive type is no longer available. |
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| Registered: May 19, 2007 | Reputation:  |  Posts: 6,730 |
| | Posted: | | | | They should be of the same size and type avoid compatibility problems.
But they can differ nevertheless.
For the following would someone please correct me if I'm wrong.
The problem with RAID is the following:
If you have for example different speed types of HDDs the whole RAID will only operate in the slowest speed of the single discs. The same is correct for the size, if your RAID5 contains of 2 1TB HDDs and 1 500 GB the total storage will only be 1TB (2x 500GB data / 500GB parity).
So for setting up a RAID5 I usually recommend to instantly buy at least two spare HDDs (for a 3-disc setup) for future use. This should ensure about 10 years. | | | It all seems so stupid, it makes me want to give up!
But why should I give up, when it all seems so stupid?
Registrant since 05/22/2003 |
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| Registered: March 13, 2007 | Reputation:  |  Posts: 1,946 |
| | Posted: | | | | They do not have to be the same size, or speed, but technology needs to be compatible. You can't mix SAS with SCSI for instance.
Keep the following things in mind. If you have 2 disks of 15.000 rpm, and one of 10.000 rpm. Your rate will perform at 10.000 rpm.
If you use one disk which has a larger capacity, the surplus space is wasted and unusable. Your RAID will have the same size of partition on each disk. | | | View my collection at http://www.chriskepolis.be/home/dvd.htm
Chris |
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 | Blair | | Resistance is Futile! |
| Registered: October 30, 2008 |  Posts: 1,249 |
| | Posted: | | | | The closer that they are in all similarities the better, but no, they do not HAVE to be the same in size or type/ The main issue is as Silence of Lambs pointed out: any array works on a weakest link principal. Add a 100GB drive to an array of three 500GB drives, and you basically end up with four 100GB drives instead. The same goes for speed, etc. The faster drives have to slow down to the speed of the slowest drives else you would end up with errors and overclocking of the slower drives trying to keep up with the faster which would make them burn out a whole lost faster. This also works on the other end, though. If you are running with four 500GB drives and one burns out (keep in mind you have to have at least three drives to maintain an array), there's no point in purchasing anything larger than another 500GB drive (and by then prices will have dropped). EDIT: Oops... way too slow. I'm the weakest link in your array  | | | If at first you don't succeed, skydiving isn't for you.
He who MUST get the last word in on a pointless, endless argument doesn't win. It makes him the bigger jerk. | | | | Last edited: by Blair |
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| Registered: May 19, 2007 | Reputation:  | | Posts: 5,917 |
| | Posted: | | | | I'm using UNRAID for my media storage. It supports a parity drive similar to RAID 5 but the difference is that you can use up to 20 drives of varying sizes, speeds, and technologies and utilize the full capabilities of each. There's no stripping involved so while you lose the speed in reading that stripping gives you but if you lose 2 drives at the same time, your entire array isn't lost like with a traditional RAID, you only lose the data on the failed drives - each drive has it's own self-contained file system that can operate independent of the other drives if removed. | | | | Last edited: by Dr. Killpatient |
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| Registered: March 14, 2007 | | Posts: 1,777 |
| | Posted: | | | | The biggest issue with RAID is not particular drives failing, but rather the RAID controller going bad. If the original controller is not matched, there stands a decent chance that the new controller will not recognize the volumes on the individual drives, rendering the entire dataspace useless. This point can't be stressed enough when planning a RAID solution. |
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| Registered: March 20, 2007 | Reputation:  | | Posts: 2,850 |
| | Posted: | | | | Quoting mdnitoil: Quote:
The biggest issue with RAID is not particular drives failing, but rather the RAID controller going bad. I've had dozens of hard drives fail over the years but not a single RAID controller, so I think I'd worry more about the cheap drives being sold these days. Also, the "REDUNDANT" in RAID doesn't mean you can stop making regular backups. --------------- |
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| Registered: May 19, 2007 | | Reputation: | | Posts: 6,730 |
| | Posted: | | | | Quoting scotthm: Quote:
Quoting mdnitoil:
Quote:
The biggest issue with RAID is not particular drives failing, but rather the RAID controller going bad.
I've had dozens of hard drives fail over the years but not a single RAID controller, so I think I'd worry more about the cheap drives being sold these days. Also, the "REDUNDANT" in RAID doesn't mean you can stop making regular backups.
--------------- Correct. IMHO there are two main categories for computer components: 1. Dead 2. Dying So nothing can replace a backup, except for two backups. | | | It all seems so stupid, it makes me want to give up!
But why should I give up, when it all seems so stupid?
Registrant since 05/22/2003 |
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| Registered: May 19, 2007 | | Reputation: | | Posts: 5,917 |
| | Posted: | | | | Nice thing about UNRAID is that you can have multiple copies of files on different drives but the UNRAID OS only presents one (combined directory tree). So if I have three drives containing the same files, I only see one and if two of those drives die, the network share of files remains unbroken. |
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