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RAID 3 or 5?

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Matt Larson
RAID 3 or 5?
on Jan 15, 2008 at 4:05:27 pm

I just bought a G-Speed XL 12 to replace my Xserve RAID and as I was looking through the manual I was surprised to see G-Tech recommend setting up the drives in RAID 3. With the Xserve RAID it seemed RAID 5 was the way to go. Digging around the forums a bit it seems people use both schemes, but what do you guys recommend for using with the Kona?

I'll be working mostly with ProRes 720p59.94 material, but I will need to be able to handle 720p Uncompressed as well.

Here are the other details:
MacPro Dual Quadcore
9GB RAM
4G/b Fibre channel hooked directly to the G-Speed XL 12





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walter biscardi
Re: RAID 3 or 5?
on Jan 15, 2008 at 4:11:29 pm

[Matt Larson] "but what do you guys recommend for using with the Kona?"

If it's fast enough, RAID 5. You give up an entire drive, but it's total and instant redundancy. At least on our systems it is.

Walter Biscardi, Jr.
Biscardi Creative Media
HD and SD Production for Broadcast and Independent Productions.

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Aaron Neitz
Re: RAID 3 or 5?
on Jan 15, 2008 at 5:28:41 pm

You still lose a drive to parity in Raid 3. Raid 5 is a little slower overall because of it's more complicated technique, and like Walter says, it's full speed even in a crash.

FWIW, I did have a regular G-Speed @ RAID 3 blow out on me once. It rebuilt itself pretty quickly and without a hitch. Was pretty happy about that.



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Tom Brooks
Re: RAID 3 or 5?
on Jan 16, 2008 at 2:04:46 am

[walter biscardi] "If it's fast enough, RAID 5. You give up an entire drive, but it's total and instant redundancy. At least on our systems it is."

Total? RAID-5 can withstand one drive failure without losing the volume. So, with one failed drive, you're vulnerable--just as vulnerable as you would be with RAID-0 or no RAID at all. That's why it's good to have a hot spare with RAID-5 and a controller that can automatically rebuild using the spare. RAID card manufacturers state that you still need a backup with RAID-5 if your data is irreplaceable.

Regarding the "instant" part, the RAID will perform at reduced speed if one drive fails. If you have a lot of drives in the set, you're going to have speed to burn, but it will still be slower until the failed drive is replaced and the RAID is rebuilt after a couple hours or so.



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walter biscardi
Re: RAID 3 or 5?
on Jan 16, 2008 at 2:13:20 am

[Tom Brooks] "Total? RAID-5 can withstand one drive failure without losing the volume. So, with one failed drive, you're vulnerable--just as vulnerable as you would be with RAID-0 or no RAID at all. That's why it's good to have a hot spare with RAID-5 and a controller that can automatically rebuild using the spare. RAID card manufacturers state that you still need a backup with RAID-5 if your data is irreplaceable."

Which is exactly what we have. Two 8TB RAID 5 Arrays with two hot spares ready to insert if the alarm goes off.


[Tom Brooks] "Regarding the "instant" part, the RAID will perform at reduced speed if one drive fails. If you have a lot of drives in the set, you're going to have speed to burn, but it will still be slower until the failed drive is replaced and the RAID is rebuilt after a couple hours or so."

The speed hit depends on the array. In our case, we have an 8 drive, 8TB array that runs approx. 500MB/s when all the drives are running. This dropped to something like 430MB/s when we popped out s drive during a 10bit 4:2:2 Uncompressed HD capture test. So in our case, it's not even noticeable when a drive fails.

This is why I purchased the array and also why we tested four different companies before making this purchase.

Walter Biscardi, Jr.
Biscardi Creative Media
HD and SD Production for Broadcast and Independent Productions.

STOP STARING AND START GRADING WITH APPLE COLOR
The new Color Training DVD now available from the Creative Cow!

Read my Blog!


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Tom Brooks
Re: RAID 3 or 5?
on Jan 16, 2008 at 4:02:20 am

Got it. That covers all the bases.


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Bob Zelin
Re: RAID 3 or 5?
on Jan 16, 2008 at 1:43:57 pm

Hi Tom -
you've got all the answers, but not much real world experience.

Tom writes -
Total? RAID-5 can withstand one drive failure without losing the volume. So, with one failed drive, you're vulnerable--just as vulnerable as you would be with RAID-0 or no RAID at all.

REPLY -
RAID 0 and "no RAID" (JBOD) are different. RAID 0 stripes all drives together, so if one fails, you lose everything. "No RAID" keeps all drives seperate, so if one drive fails, you only lose the data on that one drive. RAID 5 is the industry standard, and has been for many years.

Tom writes -
That's why it's good to have a hot spare with RAID-5 and a controller that can automatically rebuild using the spare. RAID card manufacturers state that you still need a backup with RAID-5 if your data is irreplaceable.

REPLY - in real life, a hot spare "ties up" an additional slot. When you create a RAID 5 group, you lose storage capacity (typically a 6TB array becomes 4.85 TB, for example). Now, take an additional drive in this 6TB array, and remove one of the drives for a "hot spare", and you have even LESS capacity. This is why many people choose to NOT have a RAID 5 + SPARE configuration. It is MUCH EASIER for some to simply have an inexpensive SPARE DRIVE on hand that they can pop in, in case their alarm goes off. Drives are cheap.


TOM WRITES -
Regarding the "instant" part, the RAID will perform at reduced speed if one drive fails. If you have a lot of drives in the set, you're going to have speed to burn, but it will still be slower until the failed drive is replaced and the RAID is rebuilt after a couple hours or so.

REPLY - the data rate of all SAS SATA RAID controllers today (supplied by ATTO, Sonnet, Cal Digit, Highpoint, etc) are VERY VERY FAST, so when your array "degrades" to RAID 0, or goes into a rebuild process, an 8 drive SAS/SATA array is STILL running over 220mb/sec, so it STILL can do UNCOMPRESSED HD without issue, so this reduced performance speed is a moot point. (and if you are doing 2K files, then I am wrong).

Bob Zelin





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Tom Brooks
Re: RAID 3 or 5?
on Jan 16, 2008 at 3:49:08 pm

The thread started out with mostly misinformation. It's better now.


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Matt Larson
Re: RAID 3 or 5?
on Jan 17, 2008 at 10:49:35 pm

Thanks for the input guys. I went ahead and reformatted the drives into a RAID 5 and I definitely saw a performance hit, but I'm still getting 180 MB/sec which is plenty fast for what I need.

Just to make sure I did everything right I pulled a drive out while I was playing back Uncompressed 720p60 and my G5 didn't drop a frame. Popped it back in and the drive started rebuilding (all while still playing back Uncompressed HD). I'll keep it hooked up to this backup machine for a few weeks, but it looks like my RAID is set to go.

I got in to the habit of keeping an extra drive packed away in a drawer in the edit room for those times when the Xserve RAID would loose a drive, so it sounds like I should plan on ordering one for the G-Speed XL as well.



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