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LaCie - firewire based RAID advice please ?

B

babbler

macrumors member
Original poster
Apr 15, 2006
41
0
Hi All,

I am on a G4 powerbook using final cut pro with multiple large video files. Even if I had the spare disk capacity, conventionally backing this up as I work is not an option. After a catastrophic external hard drive failure, I bought a LaCie 500Gb with 1 firewire 400 and 2 firewire 800 connections.

But realise that I am still living very dangerously with everything on 1 disk and suspect I need a RAID system. After some Googling I think I know what RAID is. I would love the safety and speed of a RAID10, but I cannot afford the 4X disk costs of setting this up. I could tolerate an interruption in the event of a disk death, as long as I could eventually reconstruct all my data. Is there an intermediate RAID scheme that would allow this ?

But what seems to be missing from all the descriptions of setting-up RAID schemes is how they work in practice. Hence a series of probably naive questions:

Can I just buy a 2nd identical Lacie and use it in a RAID scheme with the first? If so, how do I physicaly make the connection? The Mac has one firewire 400 connection, can I join the two Lacies by putting a firewire 800 cable between them? What if (when) I need more capacity? Can I just daisy-chain additional pairs and configure them as addiional arrays?

Is the 'definition' of the RAID within the external disks or on the host computer? Often I need to connect the disks to different Macs, can I continue to do that? just plugging and unplugging as normal?

What happens when 1 disk dies? Will I know it has died ? Can I continue working on 1 disk until I get a new one? Do I then just plug a new disk in and leave the mac software to recognise it and realise that it needs to fill it with data ?

Sorry for the long and rambling question - all help and advice gratefully received.

Thanks
 
Couple of things:
What is your tolerance for data loss? Would it be devastating if you lost the work you had done in the previous minute? Hour? Day?

If you can tolerate a day's loss, then you don't need a RAID, you need a scheduled backup system.

If you need to recover up to the minute or hour, then you need a RAID _PLUS_ a scheduled backup system.

A RAID only protects against single mechanism failure. It doesn't protect you against procedural losses (accidentally throwing away or overwriting a file -- the Oops gets done to both the original and the mirror simultaneously), and it doesn't protect against data corruption that happens while writing.

You could use the OS to set up a RAID with two Firewire drives; the disadvantage here is that you will then be pushing 2 x the data down the narrow Firewire hose, which is already at capacity reading and writing huge video files. You are adding some CPU overhead as well, so expect that things will slow down. BareFeats.com has written extensively on RAIDs, and they recommend installing a second Firewire controller to split the work -- in a 15" or 17" Powerbook you can install a PCMCIA card Firewire controller.

The other approach is to have a single enclosure (from LaCie or a number of other co's) which actually has a RAID hardware controller in the enclosure, and a single Firewire cable to the machine. This way, the original amount of data is going to and from the enclosure, and the controller in th enclosure takes care of the mirroring part. Of course, if the power supply of the enclosure or the internal controller break down, you're dead in the water.

If you have the money, this is what I would do:

Get a PCMCIA SATA controller card, and an external SATA enclosure with removeable drive trays. This allows you to have multiple drives, for backup and for putting different projects on different drives. It also gives you a bunch more bandwidth than Firewire will. Firmtek makes this stuff and it's Mac comptaible. I have several Audio and Video studio customers using these eSATA solutions.

Then decide whether you want a RAID 1 (mirror) or whether you can tolerate some loss, and do a periodic mirror copy.

If you want a RAID with higher speed yet, you;ll need to go to the expensive larger arrays with hardware RAID controllers.

Thanks
Trevor
CanadaRAM.com
 
Thanks.

I think that an array based on totally independant drives would be safer for me. What happens if the power supply in the array box fails ? Or something goes wrong with its own hardware? I realise that no data would be lost, but I am living a long (long) way from 'civilisation' and a replacement could take literally months to reach me. The nice thing about a system based on small standalone HDDs is that any replacements could be carried in by travellers relatively easily.
 
babbler said:
Thanks.

I think that an array based on totally independant drives would be safer for me. What happens if the power supply in the array box fails ? Or something goes wrong with its own hardware? I realise that no data would be lost, but I am living a long (long) way from 'civilisation' and a replacement could take literally months to reach me. The nice thing about a system based on small standalone HDDs is that any replacements could be carried in by travellers relatively easily.
Click to expand...
If at all possible, I'd try to buy a identical drives and enclosures (to make replacement of parts easier) and at least one backup (spare) drive and possibly enclosure, given your distance from anything. I'd also consider a cheap, slow, high-capacity backup drive to supplement the RAID. As CanadaRAM mentioned, you need some way to overcome operator error even if the drives never fail. You can get 320GB drives plus cheap enclosures for not much over US$100.
 
Thanks for these replies - I now have a better understanding of the issues.

I had not realised the obvious fact that there would be a big performance penalty in any kind of software-defined RAID based on independent drives. Disk access is the limiting factor in almost everything I do. So for now I will simply get a second identical 500Gb drive and do overnight backups. For the future, I will look at the 1Tb G-RAID pro which could then be backed-up overnight onto the two 500Gb Lacies.
 
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