RAID 0 or RAID 1?

[Karel Bata]

I've got a RAID 0 set-up here, but I worry about a disk failure.

Having read up on RAID I've decided that the best set-up, on a budget, is RAID1. You don't get the increased write speed, but you get nearly double the read speed, and (most importantly) you get a constant back-up.

However I was just reading the System Requirements for Aspect HD and they say you should have RAID 0.

Any thoughts on this?

[Graeme Nattress]

RAID 0 gives you most speed, but if you loose one drive, you've lost the lot!
RAID 1 is mirroring, which means you could loose either drive and still have all your data. It doesn't help write speed at all, but you might get better read if it's split between the drives.

RAID 3 or 5 give redundancy - loose one drive in a set and you're ok - you need a 3 drive set minimum. You will also get some better write times and read times too. If you need more than that, stripe a pair of RAID 3 or RAID 5 drive sets with RAID 0, giving RAID 30 or 50 which can be used for uncompressed HD, and you've got some redundancy.

Graeme

[Rob Lohman]

The reason they are telling you to get a RAID setup for AspectHD
is that HD is more data to transfer than simple DV. So if you use
it with HD RAID 0 might still be a good thing to have.

Whether or not one of the safety RAID options for you is a good
thing depends on what kind of safety you are looking for. A RAID
system (NONE!) is **NOT** a BACKUP!! Never EVER confuse the
two things. This is a known thing in the "professional" world. Let
me explain the difference to you:

1. a (good) backup protects you against varying levels of data loss (this WILL include deleting files and usually [depending on the safety level] includes stealing and fire [ie damage to a building] as well

2. a RAID (not RAID 0) system protects against a harddisk failure (and only that)

The MOST important difference (for prosumers such as ourselves)
is that if you DELETE files from your RAID set they are basically
GONE (yes, I know about undelete tools, but that is NOT a method
to insure (your) backups!!). So if you want safety against failures
like:

1. deleting files on accident
2. virusses deleting content
3. some other filesystem level corruption
4. mainboard/IDE/RAID controller failure

In these cases you will need a seperate backup system like an
external harddisk (only connected when backing up), DVD's, tape
or an another computer (could even be remote over the internet).

If you just want to protect against a single harddisk failure and
don't care about the list of things above then a RIAD 1, 3 or 5
solution would be good to work with. However, if you also need
speed you need to look into a RAID 10 setup (4 harddisks) which
most (cheap) cards do not support probably.

Just in case someone is wondering how companies can protect
against some of the other things I mentioned: most companies
make sure there tape backups are off-site (not in the building),
so if a fire where to breakout or someone would steal the
computers the data would be safe (some companies backup over
the internet or private networks to other branches for example).
The futher these copies are away the more safe your data is
(together with more copies).

[Karel Bata]

Tests have shown that you do get better write speed with RAID 1 - if you have data packets of the appropriate size. I rather like the idea of never having to back up.

My main question is why Aspect express a preference for RAID 0. With SATA drives I would have thought the increased write speed of a RAID setup is redundant.

[Rob Lohman]

Karel: check my post (we posted at the same time)

I do not see how RAID 1 would increase your writing speed
since it still needs to write the EXACT SAME data to both drives.
With striped (RAID 0) it can split 50% over one drive and 50%
over one drive to speed up the writes. Where are these "tests"
you are referring to?

I'm suspecting a higher write speed might be due to better
controller design in the RAID card or more cache memory or
something (in RAID 1)

[Karel Bata]

Thanks Rob.

We posted at the same time.

And I'm sure this very forum uses the same security you are talking about.

Yes, a hard copy on to another remote platform or media is the best protection, but if you're lucky a fire etc will never happen. And if you're sensible, like I am, your precious data is kept well away from any possible viral sources. What I worry about is the day one of the hard drives fails, and - sods law - it'll have been a while since there was a proper back-up.

Also, recovering a full RAID 0 set-up from drive failure is quite a procedure. Whereas my understanding is that with some RAID 1s you just slot another hard drive in, mirror the still functioning one across, and you carry on as before (having just gained a few gray hairs!).


Pity there's no proper smilies here :-)

[Karel Bata]

Quote: I do not see how RAID 1 would increase your writing speed since it still needs to write the EXACT SAME data to both drives.

Opps! I meant read speed. Sorry.

In fact the write might be marginally slower due to the PC having to work harder. But that's not where any bottlenecks going to be is it? So I doubt you'd see a difference. Anyway since everything I've done so far comes in on DVD that's never been an issue for me.

I'm just wondering if writing to disk from an HD source might need more speed than a SATA drive can offer.

Or is writing to disk from an HD source just data transfer, and hard drive write speed is not an isssue at all? In which case RAID for write is redundant.

[Rob Lohman]

In this case RAID 1 could work for you, but if you are also working
with HD material (are you?) with AspectHD you are going to have
a "problem" if you also want/need RAID 0. I don't know whether
you need it, since I'm not into AspectHD myself. Again, RAID 10
might be a solution, but I'm not sure whether your system will
support that (and you need 4 harddisks).

Why not simply keep your RAID 0 setup and add a third harddisk
and use that as a backup medium? The workflow would be like this:

1. capture all the footage (or copy from DVD) to your RAID 0 array
2. you can copy this footage to your backup harddisk if you don't trust the tape/DVD or don't want to recapture if something happens (or DVD needs to go back)
3. after a day of work copy all your changes over to your backup drive (usually these are just the small project files, but may include any other media you created in external applications like paint, audio programs or DVD authoring systems. In other words every element you cannot recover from your original media).

In this mannor you do not have to choose between RAID 0 or 1
(assuming you need 0 for AspectHD), don't have to buy two new
harddisks (just one) for RAID 10 and still have at least some
security etc.

The write (and read) speed of a harddisk is the same, no matter
what the source is. With RAID 0 you are increasing both (although
NOT twofold!!) since it can read and write in parallel. With RAID 1
you are not increaseing write (as you know) but are increasing
read times (with a good controller).

So copying your HD could take less time in RAID 0 if your single
harddisk was slower than your DVD drive (I'm hoping for your
sake it ain't). But since your drive should be way faster than your
drive you will see no difference in writing speed in this case (nor
with capture since DV always comes in at realtime from tape).

You might see performance increases for writing when you are
copying from another high speed medium like an external
harddisk. Your DVD authoring application might be a tad faster
as well when compiling the DVD image since it can read the
source files faster and write them faster as well.

Read speeds (ie, your NLE or authoring application reading the
source files) should increase due to the RAID 0 setup.

I hope this all makes some sense.

[Karel Bata]

Mmm.. Thanks for the truly comprehensive reply. I hope other readers find it useful too.

And of course when your digitising you're doing it in real time. I forgot. (I need an 'embarrassed' smiley here) So I need the fast write speeds.

My setup currently here is dated, but works fine with the relatively low res I generally do stuff in.

But I'm thinking of buying the new Sony HVR-Z1 when it's out, so my system needs an upgrade - even if it's just for the digitising. I've got a Lacie external hard drive now (it's two drives actually - internally it's a RAID 0), and since it has firewire 800 I think I'll go with your suggestion and use it for backups on top of a RAID 0 I'll install in the main PC.

Is there any way you know of automating this backup process? Ideally something where you hit a button in the task bar when you go off for a cup of coffee?

Just wondering...

Shame to be kicking out the old drives. They were objects of desire once. Heh heh.

[Rob Lohman]

There are a ton of backup applications available to do such
backup tasks automatically or at the push of a button. If you
know how to write batch scripts onder DOS you can even very
simply automate that with an XCOPY32 that way if it is a simple
copy of a couple of directories from one drive to another.

[Karel Bata]

Oh that I can do.

I was thinking of something that could be run while Premiere is still open, and that wouldn't write one whole disk to another, but rather detect any recently changed files and copy over only those.

It's a shame that progs like Premiere don't have an option with which you can specify a second 'save as...' location on a backup drive, so just hitting ctrl+s would save the currently worked on file to two different locations, thus backing up your work as you went along.

Or something else that functioned a bit like that would be great.

(Maybe I should patent the idea quick!)

[Rob Lohman]

A good backup or perhaps file replication software should be
able to do what you want (including copying files that are in use).

[Karel Bata]

Oh, we've moved house.

I've thought of a workaround (which others here might find useful) which is very simple.

In settings/folders I click 'remember folder settings on startup'

I then leave an icon of the back-up hard drive on the desktop, along with the folder with my project files (a shortcut won't do, so it'll have to be an open window showing the folder).

Then when I'm in Premiere and fancy a break, all I need do is click ctrl+s, wait a few seconds, minimise the window, drag the project folder to the backup drive icon, and it will start to copy. When the dialog comes up saying 'you already have a folder with the same name...' click 'yes to all' and go and make a coffee.

When I come back everything is saved and backed up on another drive. I click maximise and continue.

:-)