What raid configuration do you guys use most or recommended?
I'm setting up a 4 bay NAS drive and trying to figure out which is the best configuration and why?
The drive will do raid 1,5,6 and 10

Thanks

With 4 disks...

RAID 0 will give you four drive speed, full capacity, and absolutely no redundancy. Lose one drive, and it's all gone.

DISK 1 - 100% to VOLUME 1, STRIPE A
DISK 2 - 100% to VOLUME 1, STRIPE B
DISK 3 - 100% to VOLUME 1, STRIPE C
DISK 4 - 100% to VOLUME 1, STRIPE D

RAID 1 will give you single drive speed, dual redundancy. Which means, total capacity will be just HALF of what you put into it, and you can lose any 1 disk no problem... and possibly 2 disks, but only if the correct 2 fail (ie. lose the master and the mirror of that master, and you're toast). Since there is no striping, speed will be limited to whatever a single disk can do.

DISK 1 - 100% to VOLUME 1, PART A
DISK 2 - 100% to mirror of above
DISK 3 - 100% to VOLUME 1, PART B
DISK 4 - 100% to mirror of above

Of note, your NAS will probably not even let you do this with 4 drives, since RAID 10 makes far more sense and has the same limitations.

RAID 5 will give you 4 drive speed, single redundancy. This means you will get 75% of the input capacity, and you can lose any 1 disk. If 2 disks fail, all data is lost. As you increase the number of disks, you only ever lose the capacity of 1 total drive.

DISK 1 - 75% to VOLUME 1, STRIPE A + 25% to PARITY
DISK 2 - 75% to VOLUME 1, STRIPE B + 25% to PARITY
DISK 3 - 75% to VOLUME 1, STRIPE C + 25% to PARITY
DISK 4 - 75% to VOLUME 1, STRIPE D + 25% to PARITY

RAID 6 will give you 4 drive speed, dual redundancy. This means you get half capacity, can lose any 2 drives, and not lose any data. As the number of drives increase you only ever lose the capacity of 2, which means this scheme is least efficient with just 4 drives.

DISK 1 - 50% to VOLUME 1, STRIPE A + 50% to PARITY
DISK 2 - 50% to VOLUME 1, STRIPE B + 50% to PARITY
DISK 3 - 50% to VOLUME 1, STRIPE C + 50% to PARITY
DISK 4 - 50% to VOLUME 1, STRIPE D + 50% to PARITY

RAID 10 is a combination of RAID 1 and RAID 0, giving you dual drive speed, dual redundancy. This means you get a RAID 0 array of 2 drives, and then that whole thing is mirrored. So it's faster than RAID 1, and can handle a single lost drive no problem, but 2 drives only if they're the "correct" 2.

DISK 1 - 100% to VOLUME 1, STRIPE A
DISK 2 - 100% to mirror of above
DISK 3 - 100% to VOLUME 1, STRIPE B
DISK 4 - 100% to mirror of above

Okay, so now for what you should use. Unless the data is absolutely mission critical, with a 4-drive array I would go RAID5. Good speed, and can lose any single drive without issue. Note that really cheap NAS devices might have poor write performance on RAID 5 and 6, but should have great read speeds.

If the data is mission critical, then I would honestly move up to something that can handle 6 drives, and put that in RAID 6 (giving you 66% capacity - 8 bays would give you 75% capacity) for best security. And I say this because it is not uncommon for two drives to fail within a short time of each other, and that's because the process of rebuilding a RAID 5/6 array after the first drive failure is very taxing on the remaining drives, and if any are slightly weak that's exactly when they'll fail - causing you to lose everything.

But if you're stuck with that 4-bay NAS, don't mind losing half your space, and want dual redundancy, then RAID 6 would be faster reading and more versatile than either RAID 10 or RAID 1 (which is best used with just 2 drives)... but will likely have lower write speeds than either of those.

Brilliant, thank you for that description. I have been looking for something simple like that to get a grip.
I am in the process of building a media server and with the amount of time I have invested in ripping my cds and about to start dvds, ITS ALL MISSION CRITICAL!

Here ya go:

[Link: synology.com]

I can't find the thumbs up button for Daniels post. But basically he nailed it.

Raid 5.

Thanks for the info.
So since I only have a 4 bay NAS and do have mission critical data stored on it and don't mind losing have my storage for a backup you day the best way is to go with raid 6?

Yes, RAID 6 is the most resilient to failure (better than RAID 5 with a hot spare) and would thus be your best choice for true mission critical data. I mean the chance of you actually losing data on a RAID 5 setup is minimal, but if it's truly mission critical data than anything you can do to minimize that risk is warranted.

Big hard drives are comparatively cheap - I would suggest sticking in the largest capacity your NAS will handle, and do make sure the drives you buy are intended for use in a RAID array (many "green" consumer drives will not perform well and may even cause issues). If you can, try to swing the lower end of enterprise-grade drives... or at least something with a warranty longer than the stock 1 year.

I myself have a 6-bay ReadyNAS Pro server with 6 x 3TB drives in there (biggest I could get when I originally started building the array), setup as RAID 6. It originally started off life as 3 drives in RAID 5, but when I expanded capacity I bumped it up to dual redundancy. Also have an older WHS system with 3 x 2TB storage drives, which doesn't actually offer RAID, but has its own internal mirroring scheme for important data.

Haven't lost any of those drives yet, but I really don't ever want to lose my data - I've still got personal documents dating back to the DOS days and emails from the mid 90s!

Be careful with counting on parity for your data drives.
If you are going to count on parity, make sure you use enterprise drives.
Check the URE rating (unrecoverable read error).
On most consumer grade drives the MTBF and URE is lower than the size of the drive. Meaning that statistically speaking, the chances of recovering data from a 100% parity drive is 0%.

I had a great article/white paper written about it, but can't find it now (Murphy's Law).
Here is another article a quick Google search came up with: [Link: smbitjournal.com]

I think I found the article I eluded to in an earlier post: [Link: zdnet.com]

Well aren't you a little ray of sunshine!

Thanks so much for ruining my day.

I was happy in my ignorance.

Now I'm not.




Just kidding. Interesting if disturbing stuff.

So far I haven't been bitten - a few drive replacements and the rebuild has gone OK. Now maybe the rebuild is ignoring those errors which I suppose is good if the majority of the data is still recovered.

Anybody know if that would be the case? I rather lose a few files then all of them.

Glad I have three separate NAS units filled with the same data - I think - I better check.
 

Depending on RAID implementation, some are go, no-go solutions, meaning that if it finds an error, it will stop and not proceed.

With that said, your choices are limited, so pick one from Daniel's extensive and well written options and go for it.

I have a fully loaded Norco 4220 file server and I'm dreading the day I have a catastrophic data failure. I'm using a software data replication with a JBOD scheme so that if I loose more than 2 drives, I still have some/most recoverable data.

http://www.baarf.com/

As has been said earlier, be sure to choose drives meant for a NAS. WD offers their "Red" drives, while Seagate offers what they call "NAS" drives.

Prices available are around $175 right now for a 4TB drive meant for a NAS. So to me, if RAID6 is available, it is a no brainer, as the redundancy it offers, and the seamless recovery when a drive fails, make it easy to live with.

The biggest issue with such a RAID6 system, is to make sure you have notification in place so that when a drive fails, that you get notified! I've seen more than one system where almost everything was done correctly... the users didn't notice the drive failures, as the system just kept running, and only upon the third failure, did they realize the problem! So, just make sure you have the NAS set to notify someone, with email, etc... and then test it by removing a drive hot, to test that the notification works, and the recovery works.

Thanks everybody for some great info.