Raid, The Dilemma

This is a bit off topic but here lyes the best folks for answers so here goes...

I have one raid stripped with 3 500 gb hitachi drives 1.5 ter),
that's internal in my G5 dual 2.5... (swift200 8 months now) Works great.

Now I'm going to use a MiniG with 4 more Hitachi 500Gb drives that will run off the same card that the internal Raid 0 runs from (no problem to do).

The dilemma,
I want to back data up that sits on the Raid 0 (not a good place for anything important, been lucky so far).
Should I set the 2nd Raid set (up to 2 ter) as a mirror for the raid 0 (Back up 0) or set it as 4 individual drives and just keep the data on them (no Back up).

I also have a 500 GB FW G-Raid external that data is on.

I would appreciate ideas here.

Hoping to hear some feed back.
Thanks

Consider RAID5. RAID5 reduces the capacity of the whole stack to roughly 75% and provides 100% backup if one drive fails.

We have two, four-drive 1TByte LaCie stacks. Each stack features about 750G of useful storage. One of the stacks went down and we were able to rebuild it with only an investment in time. Total bytes lost, zero.

The other RAID techniques give you either very high speed, or half capacity (or both) with a very high investment in hardware.

If you lose more than one drive under RAID5, you're dead, but that's playing the odds and they can be pretty good.

We did have one problem where The Cabinet went down. But again, we changed the cabinet and everything came back up with no trouble.

Koz

RAID 5 is considerably slower than RAID 0, but 0 is open to any failure loosing all data.

The latest SATA RAID II cards from HighPoint-Tech.com allow for hardware striped RAID's that won't go away when upgrading you operating system software. RAID 10 is the safest and fastest as it is a mirror of stripes with the RAID 0 speeds available. Also takes twice the number of disk drives as RAID 0 or 5.

How do you set up a raid 5?
Apples disc utility can't i believe.

I looked at softraid and as good as I hear it is I dont know if it does 5 either.

What I really don't like about SR is it looks a bit complicated to those with limited experience with raid technology and they have NO tech support even for 90 days.

What they call tech support is email and make an appointment for a return call or return email back.
Usually when you need some assistance it's NOW ot in 3 days.

That doesn't say much for that company.
Are there other alternitives?
Thanks,
Arnold Farran

Just a few words about RAIDs and data security, maybe it helps
Data loss can happen any time, you just can make it more likely or less
0 = data striping, fast and unsave. With each drive you add it is more likely you will lose data one day
1 = data mirroring, quite save but no real speed enhance, though there could be some since bad blocks are handled way faster. Still if one drive in each of the mirror block fails you still have some trouble to get your data back
2 = no idea
3 = a good way for video, 3 drives minimum needed, it's data striping like level 0 on the drives 1 to (total amount of drives-1) and parity data on a dedicated drive, but requires that the dedicated drive is very fast and reliable, since the usage of this drive is very intensely.
3+ = same as 3, plus an additional drive in case two drives fail, I use this all time and never had a data loss, though I had a failure of two drives
5 = data striping and parity data on all drives (striped), this is the best for Internet servers and and databases, since small blocks of data can be handled more efficient than with level 3. The storage amount (or loss) are the same as with level 3
5+ = also an additional drive
6 = I've forgotten

Depending on the hardware you use you can combine those levels, to make them more secure or fast.
So for example you can stripe 3+ RAIDs by software to get more speed or you can mirror them to make them more save.
Software based RAIDs normally only support level 0 or 1.

Using a dedicated hardware to do level 3 (or maybe level 5) is the best comprise of speed and security, adding a "+" to that level makes it saver and additionally reduces downtimes again.

Regards
Andreas



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Andreas,

Thank you for the great explanations of the different Raids.
Most helpful.

Couple more issues that confuse me:

Raid 1 (mirrored) .. backs up a Raid 0 (stripped)?

I assume that the data now is in two places, The orig on the Raid 0 array and now on the Raid 1 array.

So keeping data on the Raid 0 is now safer? correct?

That being the case, what difference does it make if the Raid 1 (mirrored) is slower? your not working from it, correct?

Next .. Can you pick and choose what files/data that you want backed up on the Raid 1 or no choice is given and all gets backed up that is written to the Raid 0 any time it's written to.
Last (I think) ... when does the backing up occur, after you finished using The Raid 0 or while your writting to the Raid 0? and if thats the case, is that what makes it slower? is it slowing your system down, like a gorilla on it's back.

"He who asks a question is a fool for five minutes; he who does not ask a question remains a fool forever." so forgive me if I a bit slow here.
I appreciate all,
Arnold



Post Edited (04-08-06 08:41)

Hi,

> Thank you for the great explanations of the different Raids.
> Most helpful.
Glad to hear
>
> Couple more issues that confuse me:
>
> Raid 1 (mirrored) .. backs up a Raid 0 (stripped)?
Right. Backup should always go to a safe storage - so not mirrored to striped. Copy the stripe volume to a mirror one would be the right way i.e. 0 to 1
>
> I assume that the data now is in two places, The orig on the
> Raid 0 array and now on the Raid 1 array.
You're right
>
> So keeping data on the Raid 0 is now safer? correct?
Not sure if I understand - assuming that the original (work) data are still a the striped (level 0) volume the are at same as safe or unsafe as before. But you have a backup!
A good idea could be to initialize the original work volume and copy the files from the backup device back to the work volume. This will bring the files into a new "non fragmented" order and makes file access faster
BUT!!!!!!!!!
there are some things you have to make sure first before doing that:
Make sure that your backup is not faulty.
Non self-contained QT movies might get problems - so check that in advance.

>
> That being the case, what difference does it make if the Raid 1
> (mirrored) is slower? your not working from it, correct?
As said it's your backup device not your working device.

>
> Next .. Can you pick and choose what files/data that you want
> backed up on the Raid 1 or no choice is given and all gets
> backed up that is written to the Raid 0 any time it's written
> to.
You can use a software like RetroSpect to do daily or weekly or ? backups. It will give you a lot of choices for what you can do

> Last (I think) ... when does the backing up occur, after you
> finished using The Raid 0 or while your writting to the Raid 0?
> and if thats the case, is that what makes it slower? is it
> slowing your system down, like a gorilla on it's back.
You have to do the backup either manually or with a software solution. In both cases it is not very clever (and fast) to use the work volume since you may change data while they are written to another device, which will lead to a non proper backup or even to a corrupted one.
The overall performance of the system naturally slows down, since it is busy copying all the files
>
> "He who asks a question is a fool for five minutes; he who does
> not ask a question remains a fool forever." so forgive me if I
> a bit slow here.
No problem

Regards
Andreas



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Andreas,
Thanks again ... this is a complicated issue for me.
Knowing as much as I can leed's to better decisions.

Why would you consider a Raid 1 (4 drives say) rather then keeping the drives as separate drives and just keep a back up on one drive, when that's full go to the 2nd, when that's full go to the 3rd and so on?

what actually is the advantage of a Raid 1? am I missing something?
Thanks for having patients.

One answer leeds to many more questions...
I have 1.5 ter Raid 0 up and running for some time as I mentioned, can I add another drive to it without upsetting the 1.5 ter and or anything on it and now make it a 2 ter even though the new added drive resides in an external enclosure bu on the same card?
A.F.



Post Edited (04-09-06 07:12)

Arnold,

> Why would you consider a Raid 1 (4 drives say) rather then
> keeping the drives as separate drives and just keep a back up
> on one drive, when that's full go to the 2nd, when that's full
> go to the 3rd and so on?
You can do that by hand, a RAID 1 will do that without your interaction and finally for 2 drives each.

> what actually is the advantage of a Raid 1? am I missing
> something?
> Thanks for having patients.
It's having a backup drive always in any situation - if you are working on a level 1 volume.
Having it as backup volume gives you twice the security to successfully retrieve backup data.
>
> One answer leeds to many more questions...
> I have 1.5 ter Raid 0 up and running for some time as I
> mentioned, can I add another drive to it without upsetting the
> 1.5 ter and or anything on it and now make it a 2 ter even
> though the new added drive resides in an external enclosure bu
> on the same card?
This depends on the controller card. To be honest I don't know much about the cards from the different vendors - I'm one of the old fashioned guys which use hardware RAIDs, put them in a room in the basement, don't hear them (no noise pollution) and just see that they work (mostly).
Any (or at least nearly all) of these RAIDs do support space extension, though this can take a reasonable time, and you really should NOT disturb them while they are working on that.
So you can buy a reasonable priced FC RAID (as an example from Fastora) with 15 slots and just use 3 of them in the beginning to get 1TB with level 3 and then then add another 4 drives to get a 2.5 TB level 3+ volume - and so on.

To get a smooth operation I still recommend dedicated RAIDs, sure they do cost more, but in case of trouble you're happy about that spent money.

As an example: a friend of mine made a indie movie with finally no money, but he succeeded to finance to get all his 16mm material to D5. He was looking for a cheap and fast enough RAID to work with the material in HD 10Bit. This was about 1.2 TB source, all of this needed to color corrected - because of the look he wanted to achieve, this summed up by rough calculation to another 2TB of needed space.
After some endless discussions he decided to build a RAID by his own using one of the SATA cards with level 0 to digitize the stuff first and then go thru it. Within the first week that RAID failed because of a bad hard drive failure. He had to take his machine and travel some 100 miles to digitize all these tapes again. Two weeks later another drive died - same story.
Though this happens extremely seldom, it can happen like every some weeks there is winner for the lottery jackpot.
He finally bought a more sophistaced RAID enclosure and had the bad luck that some of his original drives failed again, but he never had to do anything else than just to walk around the corner and buy (or change) a hard drive.

Hope this confuses not too much
Andreas



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