[ Updated July 29, 2014, to reflect additional comments from Promise Technology. ]
A RAID (Redundant Array of Independent Disks) collects a group of hard disks into a single enclosure to provide great speed, storage capacity, and/or security than is available with a single hard drive alone.
Storage is an essential element of media editing – both audio and video – and I enjoy testing and reviewing the latest storage hardware as it comes out.
Recently, after posting a review of a new RAID from OWC, Robin Harris (www.storagemojo.com) wrote a very intriguing comment:
“On the issue of RAID 0 vs RAID 5 on low-cost arrays: I prefer RAID 0. Based on the best available research evidence, all hard drives have an MTBF of ≈300,000 hours or an annual failure rate of 3-4%. This means that if you use RAID 0 you have less than a 1 in 5 chance of a drive failure in any given year with a 4 drive array. However, low-cost arrays like the ThunderBay only have one power supply and, in my experience, a higher failure rate than any one drive, or even any four drives.
“Therefore, in my experience – which includes working in large storage companies, so I have a large sample – a small array is as likely to have a power supply failure as a disk failure. And when that happens you’ll have to stop work until you get your backup loaded on a new array. So the extra safety of RAID 5 is more apparent than real, and it’s slower than RAID 0.”
Everything I thought I understood about RAIDs taught me that RAID 5 is better than RAID 0. On the other hand, I didn’t have Robin’s experience. So, I sent his comments to storage experts I knew in the industry and asked them to comment on it:
I found the discussion to be fascinating, which is why I’m sharing them with you.
MY QUESTIONS
Based on Robin’s comments, I asked everyone the following two questions:
COUGHLIN & ASSOCIATES – www.tomcoughlin.com
Tom Coughlin heads a consulting company, Coughlin & Associates, that covers the entire storage industry. Tom, himself, is an engineer with over 30-years experience in media and storage technology.
Thanks interesting observations. Here are some comments:
First of all to use RAID 5 you need at least three HDDs. Thus we need to compare 3+ HDD RAID 0 vs. 3+ HDD RAID 5. RAID 0 stripes the data across all the drives and the failure of any one drive will cause significant data loss. The actual MTBF depends upon the drive type. HDD MTBF ratings can vary between 300,000 and 1.2 M. This may improve the odds that you will have a drive failure, but in a RAID 0 configuration if you do have a drive failure you will lose data. In RAID 5 you can lose one drive and assuming that you can rebuild the data from the failed drive on a new drive before another drive fails you will not actually lose any data. A low cost array may have a power supply that would fail more often than a drive but if the power supply fails in the wrong way at the wrong time it could corrupt one of the drives. If that failed drive was in a RAID 0 configuration you would have data loss even if you fixed or replaced the power supply. In the case of RAID 5 if you replaced the bad power supply you could recover the data from that failed drive.
So the data security on RAID 5 is real but there are other ways to make your data more secure. If you want the speed of a RAID 0 system you can have two of these that mirror each other–at double the cost of course. That way if one RAID 0 system goes down you have another copy and can rebuild it on a repaired RAID 0 system to retain the redundancy. Also there are systems with double drive parity vs. single drive parity (RAID 6), so two drives have to fail at one time to lose data, but this probably only makes sense for larger storage arrays. Also if you really want to avoid system downtime (vs. data loss) you may want to have power supply and other critical component redundancy or to have backups or mirrors of your storage system.
So it depends upon what sort of odds you are betting on… In general I suggest having data in more than one place and accessible quickly in case your primary storage goes down.
OWC – www.macsales.com
OWC was founded in 1988 and has long been a supplier of products for the Mac, including manufacturing their own storage products. Larry O’Connor is the CEO and founder of OWC.
Well – I’d hit that a couple ways….
One bit – we already have a lot of customers RAIDing across two ThunderBays with up to 8 drives. This is very stable and easy to do too. Some doing 6 drive RAID 5 and 2 drive RAID 1 mirror even for important archive. In any event – with 6 drives you pretty much max out Thunderbolt 10Gb/s under RAID 5… and with 8 Drives you pretty much get there with Thunderbolt 2 20Gb/s as well… so – performance is at max while still having redundancy where a little additional performance is sought.
As for the whole drive failure bit and power supply mention. The probability of our power supplies failing on any shipping unit today is a tiny fraction of the probability of a drive failure of a drive less than 1 year old and that is the case for years with the power supplies we utilize and applies 3 years from now adding a new drive to a enclosure as well (tiny faction probability to power supply failing vs. a brand new drive failing within first year)… and of course, the probability of a drive failure goes up substantially over time as well. We go overboard with highly rated, robust power supplies with all of our solutions because of the importance there of. I’ve seen competitor multi-Drive 3.5″ based RAID solutions that have a weaker/lower output than our SINGLE drive 3.5″ solutions… and for sure, that is a factor in those crap solutions failing earlier than they would (and other component factors too..) with a better power supply.
With any SoftRaid created array – you can move the drives to nearly ANY JBOD enclosure or even direct SATA bus bays – or a mix – and access / mount / use the RAID set. So – in the event you did have an enclosure failure – as by design we’re open vs. a closed/proprietary – there is great flexibility in accessing the RAID set via other available hardware and of course a replacement enclosure as well.
If I have been working on a project all day and I lose it cause a drive fails – I’d argue there is a high cost for the time and creativity vested that is lost in such an event and that the loss there of is preventable with a RAID 5 instead. Many applications can’t use all the speed that a RAID 0 would give vs. a RAID 5 in the first place too… if you’re working real-time, higher disk I/O isn’t making you get it done faster as real-time is real-time.
The tradeoff of a little performance to have that redundancy seems a very favorable one in my opinion. It’s no different than why driving without insurance is rather unsettling vs. having that safety net. Probabilities don’t matter when you lose something that you put time into… and, while a RAID 5 is not a replacement for a good backup strategy and rather should be a part thereof, a lot of pros aren’t the greatest with timely backups and that’s just another place where the RAID 5 can save someone’s butt.
Fixed hardware raids, by comparison, offer less performance and far less recoverability in the event the hardware itself fails vs. a drive.
Regardless – I’d always go RAID 5 vs. RAID 0 for anything that had work output. A RAID 0 as a scratch disk with the output going to another redundant volume, ok… but with a RAID 0 – it’s just one badly timed drive failure that could cost someone exponentially more than the cost of the actual hard drive that failed. Oh – and of course one other serious SoftRaid feature is the intelligent drive health monitoring and notification. If you’re going to go RAID 0 – it’s nice to the possibility of a decent warning before the worst happens… and in general with RAID 1, 4, 5 too – nice to have the ability to be proactive there as well. Most drive monitoring we’ve seen in other hardware and software is typically telling you the drive has a problem at a point where a failing drive may already be causing issues / slow access / etc – if you have such warning at all. SoftRAID has well developed predictive health monitoring that is far better, in what I’ve seen, for giving a real opportunity to avoid disaster before there are even signs of such occurring.
That’s my opinion. 🙂
PROMISE TECHNOLOGY – www.promise.com
Promise Technology is a global leader in the storage industry, and well-known amongst creative media professionals for its Pegasus2 desktop RAID storage and VTrak RAID storage subsystem – both of which are sold through Apple. The company makes RAID 0, 1, 5, 6, 10, 50, 60 systems.
Elaine Kwok, Product Marketing Manager for Promise Technology, writes:
For prosumer or professional backup, RAID 5 redundancy is much preferred for HDDs, or spinning disks. Anytime one disk goes down, which probability of happening can be quite high, all your data is lost. With a Pegasus2 RAID 5, 6, or 10 solutions, what you have is a robust portable solution with the versatility of ingest from a camera, to the capability of directly migrating this data to a shared storage solution for multi-user collaboration — via Sanlink2 8g FC and the VTrak a3800 storage appliance.
RAID 0 solutions tend to be for single users who are extremely cost sensitive and just require basic storage. While acceptable for SSD solutions, there is a very high risk for data loss with HDDs, or spinning disks. There is minimum protection, and this level of protection is usually fine for the average consumer. Many typical desk to basic storage only utilize RAID 0 to keep costs down. However, any consumer who wants peace of mind without having to make an additional duplicate copy may find the additional investment for a RAID 5, 6, 10 solution worth it for what might be at risk for loss.
The trend is that while video editing teams are no longer in the 20-30’s smaller workgroups are emerging that require shared storage at a subsystem level, with the same kinda of availability. Most consumer grade products can not cover this space. But Promise’s expertise is in the subsystem space with the VTrak x30 – and the VTrak A3800 based on this subsystem addresses this shared storage space. The Pegasus2 with RAID 5 is the DAS solution that can make this linkage.
Victor Pacheco, Director of Field Applications and Support at Promise, adds:
[Back in 2007, I wrote a white paper on using Raid 50 or RAID 60 in high-capacity RAID systems. It’s about the high probability of disk drive failure. Back then we limited the number of spindles per RAID 5 and RAID6 to 16 drives. Now we support up to 24 in our VTrak-series products. Since then our error handling has improved and drives are less and less prone to failure but these do happen.)
[The answer is that it’s] about what the customer is willing to afford.
1. Which RAID should media producers use – RAID 0 or RAID 5… and why?
Promise today only ships with RAID 5 for spinning disk, it also offers advanced configurations with RAID 6 (in all Promise products, including Pegasus series).
RAID 0 is suited for solid state media.
What criteria should we use to choose RAID 0 or RAID 5 — assuming the RAID supports both?
For spinning disk I would say RAID 5 at a minimum. Specifically if the customer does not require the additional bandwidth and can afford to simply reinitialize the array in the event of a drive failure with RAID 0.
G-TECHNOLOGY – www.g-technology.com
G-Technology delivers premium storage solutions for audio/video production, photography and the professional content creation market. The company makes both RAID 0 and RAID 5 systems. Mark Anderson is a solutions engineer at G-Technology.
1. Which RAID should media producers use – RAID 0 or RAID 5… and why?
Whether or not the chance of a power supply failure were as great as that of a drive failure (which I do not believe to be true, though I don’t have data to confirm that), there is still a big advantage to RAID 5 in terms of data protection:
If you have a power supply failure, whether running RAID 0 or RAID 5, you can, for the most part, swap the drives into another like enclosure (or replace the power supply) and continue working without data loss – it will only cost you the time it takes to fix or replace the enclosure.
If, however, you have a drive failure, it’s a completely different story – in RAID 5, your data is still safe, and you can continue working (plus, once you swap the failed drive out, the array will rebuild in the background); in RAID 0, however, you’re sunk. You lose everything since you last backed up. Plus, depending on the form of back-up you’re using (tape, a slower drive or drives, etc…), you also lose the time that it takes to copy all of that data onto a new array before you can get back to work.
2. What criteria should we use to choose RAID 0 or RAID 5 — assuming the RAID supports both?
I choose RAID 5 whenever possible. I would only choose RAID 0 if the requirements of the project I was working on dictated the highest level of performance possible (and exceeded the performance of my system in RAID 5). And if I did that, I’d make sure I also had a relatively fast backup system constantly connected and synchronizing frequently via Chronosync or a similar application.
DROBO – www.drobo.com
Drobo makes a variety of storage products, most of which are RAIDs using their proprietary RAID technology, which most closely emulates RAID 5. Mark Fuccio is their business development manager with long-time experience in the storage industry.
You always ask good questions. I’m happy to share some facts, deductions, and opinions.
Fact: With RAID 0 a drive failure will trigger loss of all data stored on the array.
Fact: Drive failure rates are not constant over time. They have a “bath tub” curve. Young drives fail at a high rate which decreases as the drive is used, seasoned drives that don’t die due to infant mortality have a low failure rate that lasts for years, elder drives have increase.
Facts: Until last year, information on drive reliability has been published in hard to find conference proceedings or obscure journals. Last November, 2013, cloud backup vendor Backblaze published information about drive failure rates they experienced in their data center: http://blog.backblaze.com/2013/11/12/how-long-do-disk-drives-last/ The article clearly shows the “bath tub” reliability curve.
Deduction: Using a RAID 0 puts data at a significantly higher risk of total loss than using RAID 5. Especially in newer arrays.
Fact: In an N drive RAID 0 array, the chance of failure is N times larger than the failure rate of [a single] drive.
Opinion: Unless RAID 0 is needed for performance reasons, I recommend all editors use a RAID 5 configuration for editing. For longer term storage, I recommend RAID 6, or equivalents, that will protect against two drive failures.
Opinion: Editors using RAID 0 must have a robust backup system to protect their work from the inevitable drive failure.
Opinion: Comparing hard drive failure rates to power supply failure rates is a specious argument, its the proverbial comparing apples to oranges. I think Robin is too focused on items that cause service interruption. But there is a world of difference between not having access to a system because of a failed supply and not having access because a drive failure triggered full data loss.
Summary: Use RAID 5 to ensure data is protected. Only use RAID 0 if necessary for performance.
SOFTRAID – http://www.softraid.com
SoftRAID is a development company, founded in 1996, that creates software and drivers for RAID systems that are used by a variety of vendors; OWC is one company that uses them. Tim Standing is the president, founder and lead developer for SoftRAID and has been developing software since 1986.
I strongly disagree [with Robin’s statement]. Out of the 25 disks we used for testing SoftRAID version 5, we had 6 fail, all with less than 1,000 hours on them (which is 6 months of 8 hours/day). While 4 of these were the Seagate disks which are now known to be unreliable (http://blog.backblaze.com/2014/01/21/what-hard-drive-should-i-buy/), I didn’t know that when I started using them. In the future, a video editor won’t know that a particular model of disk is unreliable when they purchase them either.
When I do the math, with 4 disks which each have a 4% chance of failing in a given year, one has a 15% chance of losing at least one of them during a given year. The calculation is the percentage chance of not having a problem (96% or 0.96) for each disk multiplied together or 0.96 * 0.96 *0.96 * 0.96 = 0.849 for 4 disks. With a 2% failure rate and 4 disks, we’re still at an 8% chance of having at least one fail in a year.
I have been using RAID volumes for my primary work Mac since SoftRAID started supporting booting in 2004. Twice during that time, I have had a disk fail. On each occasion, I was under deadline pressure, once to get a new version of SoftRAID out and the second time on a deadline for a magazine article. It was so reassuring to be able to just keep working, order the replacement disk and know that I could repair the degraded RAID volume when I had time after the deadline rather than having to go reinstall a new OS, reinstall all my apps and restore my work from the backup on the server.
Robin has been unusually lucky with disks.
One more comment: SoftRAID has the ability to detect when disks are much more likely to fail. This feature, which we call predicted disk failure, is based on a study by Google of over 100,000 disk drives and uses the SMART parameters they identified as being predictive of disk failure (http://research.google.com/archive/disk_failures.pdf). Of the six disks which failed during testing, 4 of them were predicted to fail by SoftRAID before they failed completely. When they were predicted to fail, they continued to function normally for a week or two before they just stopped working completely. The SoftRAID Monitor indicator in the menu bar turns red when a disk is predicted to fail so you know that there’s something wrong.
[Finally,] in the two years of testing and development of SoftRAID version 5, none of the 6 JBOD boxes we have used has experienced a power supply failure.
If you want to take this one step further, I would advocate using RAID 1+0 storage over RAID 5 for truly critical work. If you have the money for two enclosures, say two ThunderBay IVs, you could put each one on a separate Thunderbolt port. This would give you the performance of a 4 disk RAID 0 array and you would be completely protected from disk, power supply and interface failures.
Yesterday, I did a quick benchmark and yes an 8 disk RAID 1+0 array does give the exact same read and write speeds as a 4 disk RAID 0 using SoftRAID. I know it’s another $1,000 but if the project is really important, it might be worth it.
We have been listening to customers requests for the past 4 years for additional RAID levels. While a lot of people request RAID 5, about 20% of them have been asking for RAID 1+0. When I asked those requesting RAID 1+0 why it was so important, they typically say that they have used a RAID 5 hardware solution and lost data on it, either from a power failure or hardware RAID controller failure. They then gravitate towards a RAID 1+0 solution because of its inherent reliability and simplicity. I know this is a whole new topic of discussion but it might be interesting for another posting to your blog.
SUMMARY
For maximum speed and given the same number of drives, RAID 0 will be the fastest. However, as you just read, for media creators, the best option is to purchase a system that supports RAID 5.
I enjoyed putting this article together and want to thank everyone that contributed – and, especially, Robin, for getting this entire conversation started.
As always, let me know what you think.
10 Responses to What's the Best Way to Configure a RAID?
I’m really looking forward to trying out Raid 5 but through an over enthusiastic response to your recent Thunderbay IV Raid 5 reviews I’m sitting here with a miss ordered Thunderbay IV enclosure having just installed the 4 toshiba drives recommended by OWC technical support. ( i missed the phrase Raid 5 when asking for advice )
The problem is that I presumed I would be getting a Raid 5 unit despite installing the drives myself. But no, the devil is in the detail and I really should have read the small print because the magic SoftRAID 5 software is only available in the pre built units, it’s not available to purchase at the moment.
I’ve yet to initialise the toshiba drives and am unsure of the direction forward. I have been told that the units are exactly the same – bar the exclusion of SoftRAID 5.
I really feel that the key OWC Thunderbay IV Raid 5 Edition page is a bit misleading in that it could state more clearly that the only way you can get a Raid 5 solution is through purchasing the preconfigured unit. there is a link saying that the Thunderbay is available without RAID software and when you click that it goes through to another page where it states that it is RAID but as I discovered not RAID 5.
I would advise anyone else purchase this unit to get the ‘Raid 5 Edition’.
I’ve contacted OWC who say the software will not be commercially available in a standalone form for a couple of months. Although it’s possible to download the beta SoftRAID 5 software from the site it requires a registration code.
I’m happy to use and pay for beta software and have contacted Softraid to see if this is a possibity.
Another idea i had was to configure the unit as Raid 0 and use it in that form until the software was available.
Do you have suggestions?
Mark
Mark:
You are correct. SoftRAID is currently only available as beta software. I’m currently using the beta version and it seems to be working with no problems.
While I can’t say anything publicly, I expect the final release of SoftRAID to be sooner rather than later.
Larry
Thanks Larry – I’ve been onto SoftRAID support and they have advised me, as you are doing , to use the beta software. At the same time they advised that I buy the latest version of SoftRAID which will lead through town automatic upgrade once the final version was out.
I had though maybe they were waiting for Yosemite but I see in the beta notes that many issues with the new operating system have already been resolved.
Actually configuring the unit into a RAID 5 couldn’t have been easier and the Disk speed test is fabulous. 396 MBs write and 549.2 MBs for the read.
Thanks again for the 2 reviews you did, for me they came at a very opportune moment.
Larry, great job getting comments from other players. And the responses are all over the map. And therein lies the problem.
First, I’ve used over a half-dozen arrays in the last 10 years, among them Iomega, Drobo, Promise and WD. I’ve found them to be reliable, but I have had multiple disk failures including a power supply failure that fried both drives in a mirrored configuration.
Second, virtually all enterprise gear – the stuff that has to keep working – has dual or even triple power supplies. So yeah, power supplies can and do fail.
My logic is simple:
– you should back up your critical data daily
– drive failures aren’t common – in a small array you have less than a 1 in 5 chance of failure in any given year for the first 3 years
– but writing to your array happens all the time, so you might as well get the maximum performance
Thus the risk is that you might lose several hours work in return for working faster for years.
If you don’t want to take that risk, then fine, don’t. But don’t kid yourself: any data stored on a single device is always at risk. Daily backups are essential. And a single power supply can bring down your entire RAID, regardless of configuration.
Robin:
Thanks for your comments. And thanks, again, for providing the spark to get this conversation started.
Larry
It’s strange that a single comment of some user which was denying the probability theory was taken that serious.
And btw can i state that a power supply of a single PC is waaay less reliable because it powers the whole PC incl. drives, video, periphery, etc?
First, long story short R5 is statistically more reliable than R0 in any ways and it ridiculous to state opposite.
Second, let’s don’t forget to change our drives in advance or be ready to have problems. Because statistically the probability of non-failure of the whole system is product of multiplication of the probability to non-failure of each drive. So the chances to have the system down would grow exponentially with the amount of drives we have plus each drive itself exponentially going to fail through time. It’s exponent of the exponent. Sounds not so reliable. We are more likely to buy all drives for RAID at the same time so they’d get old together and could fail almost together – so once again don’t forget to change the drive before it’s too late if you want to keep your nerves and work.
Third, i really don’t understand why are we talking about R5 and R0. Do the drives cost thousands to have them as much as you need to have fast RAID1+0 massive? As you may know R1+0 is a mirror – so back up is just a full copy of the certain drive. R5 doesn’t work this way. Moreover some of the drive manufactures even doesn’t recommend the R5 due to huge rebuild time when one of the drives failure. The more capacity of the stripe the more rebuild time. It literally could take days easily. And remember all drives are in hard use during rebuilds. And the probability to loose the drive is pretty high during rebuild.
So summarize. RAID1+0 – fast, pretty reliable, and easy to maintain – you may have full reserve copy of two drives and then watch only changes on disks making difference back ups while failure means you just copy one full size disk or copy from reserve if you have it and if second mirror disk failed during recopying.
Yes it’s more expensive but does your time investments in work cost something and does your neurologist would take care of you and your stuttering for free after you’d loose all your RAID5? 🙂
Yruss:
Thanks for your thoughts. And, yes, I read all the comments and found the RAID 5 vs. RAID 0 an excellent opportunity to learn more. As an example, just look at all the comments for this article.
Also, until recently, RAID 5 units that were large enough to support media professionals were EXCEEDINGLY expensive – far more than most productions could afford. The new, lower price points make considering RAID 1+0 reasonable for the first time.
I know that in my business, a single RAID 5 is affordable, but the two RAIDS needed to create RAID 1+0 is not. It would be NICE to have RAID 1+0, but the checkbook says no. In which case, we need to look at other options.
Larry
Larry:
I don’t know what exactly we’re talking about here because the industry and the industry are two big differences as we say in Russia.
Simple edit, multicam edit, VFX, 2K raw or 8K raw would take different amounts of space through work. But whatever they take i can’t imagine situation where 10 bucks for something would be less preferable than 6 bucks for nothing if you’d loose R5 massive with all work. Maybe if you’d explain me what exactly you’re talking about i’d change my mind.
But for now i look on the R1+0 massive like a necessary evil – it’s investments in the reliability. How would you make this investments work is another question.
P.S. Sorry for my arrogance – but do you understand the thing that RAID1+0 could be build in one RAID box? Let’s say we use one Promise Pegasus R6 18TB RAID. We can make: 15TB in R5 or 9TB in R1+0. We do not need two boxes for RAID1+0.
P.P.S. The CAPTCHA code almost always expires to the moment you finish writing average length comment.
Forgot to add.
There’s such thing as a Unrecoverable read errors. (URE) present as sector read failures. Different types of disks(desktop, server) have different rate of it – for desktops and enterprise it’s usually 1* 10^14, server 1 * 10^15(the higher is better), there’s even 1*10^16.
4TB drive contains 8/25*(10^14) bits. If we rebuilding 4x4TB drives RAID5 massive we’d transmit (4 * 8/25) or (32/25) or 1.3* (10^14). Let’s compare this to UBE. 1.3>1(!). Which means that we guaranteed to lose one bit which automatically means the lost of the whole massive. You would not lose it only if you’re extremely lucky because 1*10^14 is only a probability which you exceeded by 30%.
And the additional advice: Don’t believe the letters and words on the HDD. Many of the manufacturers write Server or Enterprise and take additional money while vibration proof and UBE is staying on the common desktop HDD levels. For e.g. Seagate doing this. So don’t forget to check PDF specs for the HDD you’re going to buy to be sure that it specs are worth the money.
With all this mentioned above and the cost of REAL server disks i see that RAID5 could even be much more expensive than the same size config of RAID1+0.
Great Article! Can you update this article at the beginning with short definitions of each RAID configuration? This link has a good explanation:
http://www.thegeekstuff.com/2010/08/raid-levels-tutorial/
Just my 2 cents, we currently use all RAID 1 for our projects with 2 drives in the RAID. I would prefer RAID 5 but the price for thunderbolt RAID 5 setups where significantly more than 2-drive RAID 1 setups at the time when we built our systems.
Maybe in the future we will migrate to RAID 5 especially since Thunderbolt versions and USB 3 versions have come down significantly.