Raid 1 with two cables or daisy-chained?

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Level 1

46 points

Raid 1 with two cables or daisy-chained?

I'm new at this, but I want to create a simple mirror Raid (Raid 1) with two identical Firewire Lacie external drives and I hope someone can answer these couple of questions:

1. Is it better to use two separate Firewire cables? That is, each cable secured in its own port on my iMac and correspondingly each cable into its own port on an individual Lacie drive (one cable going from computer to external drive for each drive), or;

2. Is it better to "daisy-chain" the two drives and only have one Firewire cable connected to my iMac.

Am I going to see any difference in performance either way? And, can I expect some degradation in performance notwithstanding which way (two wires or a daisy-chain) I connect the Raid.

Thanks, I appreciate any help you might give me.

iMac intel, Mac OS X (10.6.1)

Posted on Oct 5, 2009 10:52 AM

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Answer 1

Oct 5, 2009 11:02 AM in response to Charles Cole

Daisy chaining will certainly not help; it's going to be slow because the bus is shared.

In general, I would not recommend RAID 1 among external drives that are not in the same enclosure.

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Answer 2

K T

Level 7

23,889 points

Oct 5, 2009 11:10 AM in response to Charles Cole

The FW bus is asynchronous - I don't consider either of your proposed configurations as better or worse - I would use one cable simply to best take advantage of the physical resources. Any signal 'juggling' will take place on the controller(s) and 'sharing' isn't going to be so much a factor since you are applying a software RAID solution.

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Answer 3

Oct 5, 2009 11:12 AM in response to Charles Cole

Hi Charcles Cole;

I think a much more important question is exactly what do you hope to gain from setting up a RAID array?

Allan

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Answer 4

Charles Cole Author

Level 1

46 points

Oct 5, 2009 11:42 AM in response to Allan Eckert

I keep the unedited video in a folder on one of the external drives. I would like to have the security of a Raid 1 (mirror) so that I would not have to manually copy from this first drive to a second drive. I don't want to lose any more speed than I have to and if cabling independently versus daisy-chaining the two external drives matters, of course I will set up the faster configuration.

I keep my video on an external drive because it's extensive and I don't want to use so much space on my iMac drive nor on my Time Capsule which backs up everything on the iMac except my iMovie Events folder - that video contained in the iMovie Events folder resides on the first external hard drive. Seems a Raid 1 would give me my only back up of my video and not burden my iMac nor Time Capsule (which is smallish).

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Answer 5

Charles Cole Author

Level 1

46 points

Oct 5, 2009 11:44 AM in response to William Lloyd

I'm curious why the enclosure makes a difference? The drives are identical. Well, I think they are identical - the are Lacie drives and I can't see inside the enclosure to see what the actual drives are. But, they are the same size and both from Lacie.

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Answer 6

Charles Cole Author

Level 1

46 points

Oct 5, 2009 11:47 AM in response to K T

Probably a dumb question here, but here goes....is there one bus per Firewire Port or just one bus that controls both Firewire Ports on my iMac? If one bus controls both ports, then your answer makes absolutely complete sense even to a newbie like me. So, would the actual gauge (thickness) of the Firewire Cable play any role if I daisy-chained the two external drives and used one Firewire Cable to the computer?

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Answer 7

Oct 5, 2009 11:55 AM in response to Charles Cole

Do you already have the drives? If not, check out the Lacie RAID in my sig. One cable, but the enclosure has a built-in RAID controller. I can't remember exactly what I paid. But, I think it was about $250.

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Answer 8

Charles Cole Author

Level 1

46 points

Oct 5, 2009 11:59 AM in response to donv_the_ghost

Unfortunately, I already have the drives, but thanks for the info.

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Answer 9

Oct 5, 2009 12:33 PM in response to Charles Cole

Hi Charcles Cole;

I was afraid of that which is why I asked my question but RAID 1 is not a backup solution.

RAID 1 is only a method to protect you from disk failure and that only.

Think about this if you are working on a video and the application crashes taking the files with it how would you recover from that with RAID 1? You will not because when the application removes the file from one drive RAID removes it from the other.

What you need is a backup solution between the two drives and NOT RAID.

Allan

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Answer 10

Oct 5, 2009 5:45 PM in response to Allan Eckert

Well, yes and no on not being a backup solution. The other common backup methods (e.g., a clone, TM, backing up on schedule, online backup, manual backup on another hard drive, thumb drive, etc., etc.) will not save him in the scenario you mention either. Perhaps there is a method, but what backup method would save him in your scenario?

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Answer 11

Oct 6, 2009 10:41 AM in response to donv_the_ghost

Hi Donv;

I don't wish to argue with you but RAID 1 is NOT a backup solution.

Allan

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Answer 12

Oct 6, 2009 10:53 AM in response to Allan Eckert

No point to arguing, but why, in your opinion, can't/isn't RAID 1 both effective as backup and as protection against the failure of one drive? And, you didn't answer the question I raised above. I am very interested in the answer to the question. It seems quite meaningful in the context of the scenario you gave.

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Answer 13

Oct 6, 2009 11:37 AM in response to donv_the_ghost

Hi donv;

Because the files are removed from ALL of the drives in the RAID 1 Array whenever a change is made there is no way to recover from a mistake that changes a file thereby leaving no way to recovery from the change. Since the ability to recover from changes is one of the primary functions for backup and RAID 1 does NOT provide that function by defintion, it is not a backup method.

Allan

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Answer 14

Oct 6, 2009 11:43 AM in response to Allan Eckert

I understand your definition and, yes, given that definition I understand why you say RAID one is not a backup method. I have a different definition so I don't agree, but there is nothing wrong with disagreement.

Above, I said:

"The other common backup methods (e.g., a clone, TM, backing up on schedule, online backup, manual backup on another hard drive, thumb drive, etc., etc.) will not save him in the scenario you mention either. Perhaps there is a method, but what backup method would save him in your scenario?

Given your definition and explanation, don't the procedures mentioned above fail to qualify as backup methods too? And, under you definition and explanation, what does qualify as a backup method.

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Answer 15

Oct 6, 2009 1:54 PM in response to donv_the_ghost

Hi donv;

This is the only definition of RAID 1 Array I know. I know of no others. Hence RAID 1 Arrays never qualify for a backup solution.

Time Machine or any other backup software that periodically copies data to another device qualifies as a backup solution because it provides the ability to recover from changes.

Allan

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