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RAID Vs. JBOD Vs. Standard HDDs
Ravengbc writes "I am in the process of planning and buying some hardware to build a media center/media server. While there are still quite a few things on it that I haven't decided on, such as motherboard/processor, and windows XP vs. Linux, right now my debate is about storage. I'm wanting to have as much storage as possible, but redundancy seems to be important too." Read on for this reader's questions about the tradeoffs among straight HDDs, RAID 5, and JBOD.
At first I was thinking about just putting in a bunch HDDs. Then I started thinking about doing a RAID array, looking at RAID 5. However, some of the stuff I was initially told about RAID 5, I am now learning is not true. Some of the limitations I'm learning about: RAID 5 drives are limited to the size of the smallest drive in the array. And the way things are looking, even if I gradually replace all of the drives with larger ones, the array will still read the original size. For example, say I have 3x500gb drives in RAID 5 and over time replace all of them with 1TB drives. Instead of reading one big 3tb drive, it will still read 1.5tb. Is this true? I also considered using JBOD simply because I can use different size HDDs and have them all appear to be one large one, but there is no redundancy with this, which has me leaning away from it. If y'all were building a system for this purpose, how many drives and what size drives would you use and would you do some form of RAID, or what?
At first I was thinking about just putting in a bunch HDDs. Then I started thinking about doing a RAID array, looking at RAID 5. However, some of the stuff I was initially told about RAID 5, I am now learning is not true. Some of the limitations I'm learning about: RAID 5 drives are limited to the size of the smallest drive in the array. And the way things are looking, even if I gradually replace all of the drives with larger ones, the array will still read the original size. For example, say I have 3x500gb drives in RAID 5 and over time replace all of them with 1TB drives. Instead of reading one big 3tb drive, it will still read 1.5tb. Is this true? I also considered using JBOD simply because I can use different size HDDs and have them all appear to be one large one, but there is no redundancy with this, which has me leaning away from it. If y'all were building a system for this purpose, how many drives and what size drives would you use and would you do some form of RAID, or what?
That said, RAID is not a replacement for proper backup. RAID is just a first line of defense to avoid downtime.
"No one likes working in a hamster wheel, and your shop smells of cedar shavings from here." - TaleSpinner
This is what you do: buy 2 drives exactly the same size and mirror them. End of story. If you're worried about a blown raid controller, then buy another hard drive and stick that on another computer and run a weekly cron job to copy everything. Right now you can get 500 GB hard drive for about $150. Get two of them and mirror them. (If you need more than 500 GB I would highly suggest encoding your porn into a different format than MPEG2) By the time you run out of space, you will be able to get 1 TB drives for about $150. Migrate over to the 2 1 TB hard drives. Repeat every few years.
With computers, the stupidest thing you can do is spend extra money to prepare for your needs for tomorrow. Buy for what you need now, and by the time you outgrow it, things will be cheaper, faster and larger.
By the way RAID 5 is a pain in the ass unless you have physical hotswap capability, which I highly doubt.
I really can't believe this made the front page. The questions are badly written, and the question itself could have been answered with some basic Internet research. RAID isn't an esoteric topic anymore, folks!
This place has really gone downhill. I thought Firehose was supposed to stop stuff like this, not increase it!
Anyways, just to be slightly on topic: there's no one answer to this question. It depends on your budget, your motherboard, your OS, and, most importantly, your actual redundancy needs. This kind of thing is addressed by large articles/essays, not brief comments.
Plausible conjecture should not be misrepresented as proof positive.
Hardware WILL get old, WILL die, and better stuff WILL become available. So it only makes sense to recognize this and plan for it.
Here's the way I do it (for a home storage server, not a solution for business-critical stuff):
Examine current storage needs, and forecast about two years into the future.
Build new server with reliable midrange motherboard, and a midrange RAID card. These days you could do with a $100-$300 four-port SATA card, or two.
Add four hard disks in capacities calculated to last you for two years of predicted usage, in RAID 5 mode. Don't worry about brand unless you know for a fact that a particular drive model is a lemon.
Since manufacturer's warranties are about one year, and you may have difficulty finding an unused drive of the same type for replacement, buy two more identical drives. These will be your spares in the event of a drive failure.
When the two years are up, you should be using 80 to 90 percent of your total storage.
At this point, you build an entirely new server, using whatever technology has advanced to at that time.
Transfer all your files to the new server.
Sell your entire old storage server along with any unused spare drives. A completely prebuilt hot-to-trot RAID 5 system, with new matching spare disk, only two years old, will still be very useful to someone else and you can recoup maybe 30 to 40 percent of the cost of building a new server.
Lather, rinse, repeat until storage space is irrelevant or you die.
Even though it was modded funny, it's good advice: if most of your data is not something you created on your own, either directly or indirectly as a part of using the computer, it's possible to replace it from an outside source if lost. All you really need a backup of is your unique data.
The advantages of RAID 0 versus RAID 1 versus RAID 5 have already been covered in detail, here, and in many books and websites.
However, allow me to address the issue of how they relate to a media center:
Firstly, when you say "media center/media server", do you mean "I just want to build myself a kickass Tivo?", or do you mean "I want to serve video for everyone in my frat house, simultaneously?"
If the former, consider that Tivos ship with 5500 RPM drives for several reasons:
1) They're cheaper than faster drives
2) They run cooler than faster drives
3) They run quieter than faster drives
4) They use less power than faster drives
5) They're more than fast enough for streaming a single video to your TV while recording another
Long story short, if you're just building a "free" Tivo with a kickass drive array, performance is *not* an issue. Keep in mind that if you're building a set-top box of sorts, the low heat and low noise features are *very* big benefits. You probably want RAID 5, and/or JBOD.
If, however, you're planning on serving video to more than a handful of stations simultaneously, you may need to consider performance. This is a vote for RAID 0 and/or RAID 10.
Now, the second axis: How important to you is this data? Really?
I've got over 300 gigs of drive space on my Tivo. Most of it is the last two weeks of television reruns (Scrubs, 6 copies of last Thursday's Daily Show, etc.), movies I recorded but won't watch, etc. There are about 10 gigs (3%) of video on there that's been saved for a few months, and frankly, I couldn't tell you a single thing on there that I'd miss if my drives went belly up tomorrow. So: do you *really* need to save all those Seinfeld reruns on a highly-redundant storage array? How *much* of the stuff on the server do you really need to keep?
Assuming it's less than 50% (in the Tivo scenario, it probably is), consider using JBOD for most of your storage, and maintaining a single backup drive, or small backup drive array. Or just backing up the good stuff to DVD.
In summary: If you're just building a Tivo, you probably don't really need the performance, or redundancy that RAID offers.
That's why you use hardware RAID. A good card will allow you to swap out drives and rebuild, or add new drives to the array, without ever needing to unmount the anything.
But the minute or so of uptime you get by not having to power down the computer is more than made up when the controller chip on your beautiful RAID controller sizzles. Using Linux software RAID lets you plug the drive(s) into another computer of a completely different chipset, boot up, and continue operations as though nothing had ever gone wrong. IMHO, this is far preferable to the effective lock-in presented to you by hardware controllers.
For me, it's all 100% software RAID 1.
I have no problem with your religion until you decide it's reason to deprive others of the truth.
Forcing this response to the top of the page, just so visitors don't think Slashdotters don't know RAID math.
I.e. 3 500 GB drives in a RAID 5 doesn't give you 1.5 TB. (RAID 0 dose that). With RAID 5 you only get 1 TB.
--= Isn't it surprising how badly I spell ?