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Hi all, I have a new 120 GB HD with 8MB of cache which I will be adding to my current machine. What configuration do I set the jumpers in? What is mirroring? I have been reading the forums on RAID set ups and some feel that there is an increased potential for data loss, is this true using the built in RAID in Apple's OS? Anyways my plans for this machine is to upgrade the processor to a dual 1Ghz from a single 867Mhz and use it for a year to year and a half then set it up as a server, so I'll probably replace the stock 60gig HD and add two 200gig HD's. That is why I was wondering about RAIDs and mirroring. Also, what about transfering everything over to the new HD, how would I do it? What would I have to do, would I need to install the OS on the new HD? Would I gain anything by putting the OS on the larger HD with the 8MB of cache? Thanks for any input. Plus anything else you could offer would be useful.

[larkost]

First off, jumper settings:

If you intend on putting both drives in at the same time, then the easiest thing to do is to put the new drive into 'slave' mode. The instructions included with your drive will explain how to do this.

Small caveat: having 2 drives will slow both of them down.. figure 10% off the slower drive's speed (yes, the faster one will be dragged down).

Next is RAID:

Mirroring means that a copy of every piece (and change) of data is stored on two different HD's. This is nice if one of them takes a digger, the other one can keep going by itself (sometimes with a performance penalty). The bad thing about mirroring is that you take a performance penalty, especially in software mirroring (what you are talking about). The penalty is proportionate to your slowest drive. I would really not recommend software RAID with your setup.

To further complicate things, this would require that you partition the drives so that you could match two partitions of separate drives up to for the raid (ie some of tour drive space would not be involved).

The second basic type of RAID is striping. In this case a pair of partitions are joined together to form a bigger space, and data is written to both simultaneously. The idea here is that a single drive can max out it's bus, and so by having two different drives on two different busses, you can get double the bandwidth. The problem with this is that if either drive goes, it takes all the data (from both drives) with it, since it is 'striped' across the drives.

Since it sounds like you are only using one controller, this is not a good solution for you, and would probably be slower than just having the two drives in there.


Executive Summary: Don't use RAID unless you know you need it.

[tooki]

Originally posted by larkost:
Small caveat: having 2 drives will slow both of them down.. figure 10% off the slower drive's speed (yes, the faster one will be dragged down).

Fiddlesticks. Neither drive will be slowed down except when the computer needs to access both drives at once. (ATA buses only allow communication with one device at a time, so the drives have to take turns.)

tooki

[Agent69]

Originally posted by tooki:
Fiddlesticks. Neither drive will be slowed down except when the computer needs to access both drives at once.

When I was running a PC, I had a PCI Promise ATA-100 bus mastering controller which connected to two ATA-100 hard drives, each on its own channel and jumpered as the primary device. Does anyone make add-in ATA controllers for the Mac?

[larkost]

tooki: I am sorry to say that you are wrong. Even if you are only communicating with one drive, you still loose speed for 2 reasons. First off the buss can only use one speed, and as with everything else in computers, low man wins. And secondly, when changing who has control over the bus you have to wait for acknowledgment from all members on the buss. Going from 2 to 3 devices is a considerable hit. The buss changes hands a lot. You are correct that this is even worse when all three devices have something to say.

Agent69: There a number of PCI-IDE cards that are available, and a group that don't even need extra drivers (this means they can be boot devices). There are even a few PCI-IDE-RAID cards that work too. Check out www.xlr8yourmac.com for their list.