Should I consider updating my 3 current NAS to use X-RAID2 (see sig below)?
OK. From the gracious help of Vanderwerwe and StephenB, I have brought back online my old Duo-v2. I chose to ?format/characterize? it using X-raid2. I do not recall being able to select 'Flex-RAID;' maybe because I only had one working hard drive installed......(?) The other 1TB drive arrived to me DOA. The RMA process is active. Yes, the DUO-v2 now runs in the 'not-redundant' mode. Fine, for the moment. It is empty after all.
The DUO-v2 now runs f/w 539-T5. It contains 1x1TB WD10EFRX drive in the left slot (HD0?). Fine, for now. As soon as I get the replacement same 1TB hard drive will I complete this rebuild and ship it off to its' new user's home. I am planning to make this NAS turn-key to the new user, so I leave its' network business using DHCP. The less time the new user spends in the Dashboard, the better for all of us! Trust me, please! I know he will read both the hdw manual and the sw manual. And, I fully expect the new user to 'play' with his new toy under the hood. I fully expect that the end user will question me in the future about 'larger' drives among other things. I'd like to think I've learned most of the answers here, but now I am a bit confused.
I know Flex-RAID is Flex-RAID. I believe that X-raid2 is an improved version of X-raid that I chose for my 3 running ReadyNAS. Am I correct? I am sure that the 'improvements are important, but, for now, not germane; and, frankly, too complex to my basic user understanding of RAID and ReadyNAS since 2009. I suppose I should be more comfortable with RAID in general, but I have to admit that most things RAID are still P.F.M. to me. I know it works. Fine. How it works is way above my pay grade! And, why I joined this community. I know that 'experts' live here. Yes, I have suggested that the new user become a member of this community. Time will tell if the new user takes the initiative to join and share with the community.
Yes, the new user does have a 500GB (465GB actual) USB drive to use for NAS backup. I am pretty sure the new user will arrive at this bright idea pretty quick!
X-RAID for your Duo (v1) uses the capacity of the smallest disk. All disks must be replaced with higher capacity disks for expansion to take place.
However since your NAS units that have X-RAID2 (Ultra 2 and Duo v2) are all 2-bay you would need to replace all disks to get vertical expansion anyway.
Also X-RAID2 distributes the parity amongst all disks whereas X-RAID uses a dedicated parity disk.
mdgm, Thank you for your share. I learned a new term again; vertical expansion. I take this to mean 'NAS capacity increase.' If so, then I am good. Yes, eventually, I intend to upgrade my 3 NAS's with 2x 1TB drives. Not so much for 'vertical expansion,' but for the fact that the 500GB hard drive size may just go EOL before any of my current half dozen begin to die. I think the 1TB size will become the new baseline for Nasware drives in the future. Yes, I know that the NAS will only use 500GB of a 1TB drive if installed today and allowed to resync. The 'vertical expansion takes place with the 2d 1TB drive goes in. Crystal clear on this. Yes, always knew that XRaid would build its' mirrored volume based on the smallest of the drive pair. This has been a basic RAID rule since forever! I will have to think about the 'distributed parity' scheme of XRAID2. ATM, I do not have a good grasp on this advantage. More research.
X-RAID is only available on Sparc models e.g. Duo X-RAID2 is available on all non-Sparc models.
X-RAID2 is better in my view.
Vertical expansion is expansion from replacing disks with higher capacity disks.
Horizontal expansion is expansion from adding equal capacity disks to empty drive bays. If higher capacity disks are added the new layer created would still be vertical expansion.
Clearly vertical expansion is the only one of these available for 2-bay models
mdgm,Thank you for your share. I learned a new term again; vertical expansion. I take this to mean 'NAS capacity increase.' If so, then I am good...
horizontal expansion - when xraid/xraid2 increases the capacity because you installed a new disk into an empty slot. vertical expansion - when xraid/xraid2 increases the capacity because you replaced an existing disk with a larger one. EDIT- same as mdgm's reply...
NASNoob wrote:
... I will have to think about the 'distributed parity' scheme of XRAID2. ATM, I do not have a good grasp on this advantage. More research.
The advantages of distributed parity apply to raid-5 or raid-6 (3 or more disks). Every time you write to a raid array, the parity block(s) needs to be updated. If all the parity blocks are on a single drive, then this can become a performance bottleneck. Distributing the parity blocks eliminates this possibility; and also evens the I/O load across the drives.
@mdgm / @StephenB, OK guys! I was so close to grasping what you shared. Then a couple of new posts, some confusion, and I'm back in the toolies! LOL! Mdgm, thanks for the vote for XRAID2. That is how I've leaned since learning about it. I asked because I am thinking of re-characterizing my Ultras as XRAID2. Unless there is some way in RAIDar/setup to query how they were set up 2 years back! I've long lost the notes for installing them. I know, stupid! :slap: I've got 'vertical expansion' down solid now. With my 3 2-drive units I do vertical expansion via putting in 2x 1TB drives (1 at a time, allowing for resync time!) I'll think more about 'horizontal expansion' because I see this as truly only providing 'redundancy' in a RAID system. Like 1 volume spread across 2 drives. I want to say a mirrored array, and/or RAID1 (but I could be wrong) which I do use on all my NAS's. To me this means everything recorded on drive 1 is duplicated on drive 2. So, even though each 500GB drive is really only 465GB logical, and, that the 2 drives together are really part of a 'fully-redundant' 465GB NAS Volume. Well, minus the overheads. OK? That is my comprehension of the PFM of RAID-mirrored. As I do not have 4-drive NASs, I would rather accept that HE and VE could take place by adding drive 3 and then drive 4. Luckily, I do not have to be concerned with this yet ATM. 2-drive NASs are all I can sorta grasp just now. If in the future, I move to 4-drive platforms, I will crawl back for more schooling, OK? I do so appreciate all your time and shares.
So... Here's what I hope is a simplified explanation of how it works:
In a real system, drives store billions of bytes each, and each byte is a number in the range 0-255. For ease of explanation, let's imagine that our drives are ridiculously small -- only large enough to store 16 bytes each -- and that each "byte" can only be a single digit in the range 0-9. I'll show how a file is stored on a single drive, on a two-drive RAID array, and on larger 3- and 4-drive arrays.
The file we're going to store is ten bytes long: "2024561212".
With one 16-byte drive, the file is stored like this:
2024561212000000 16B usable, 6B free (blue is our data, green is free space)
With two drives, the data is mirrored. This arrangement is called RAID1:
If one drive fails, you can still read your data from the other drive. When you replace the failed drive, the NAS will rebuild the array by copying data to the new drive from the old one:
You'll often see this type of expansion -- replacing small drives with bigger drives -- referred to as "vertical" expansion. Unfortunately, I've chosen to diagram each drive as a horizontal row in order to save space in this post, so in my diagram the expansion looks horizontal. Sorry about that.
Anyway... With three or more drives, we can achieve single-drive redundancy without wasting half of our physical array. To do that, the data is striped across the drives and parity is added. Parity is extra data computed from the original data by some formula; for this example, the formula we'll use is "sum the bytes in each column, then subtract the rightmost digit of the sum from nine". This striped-with-parity arrangement is called RAID5. Here's how it looks in a simplistic form with all the parity on a single drive:
See how that works? 2+0=2, 9-2=7. 2+4=6, 9-6=3. 5+6=11, rightmost digit is 1, 9-1=8. 1+2=3, 9-3=6. 1+2=3, 9-3=6. 0+0=0, 9-0=9. And those are the first six parity digits on drive 3: 738669.
The cool thing about this arrangement is that it's not just drive 3 that is the parity for drives 1 and 2; every drive is the parity for the other two drives. You can check this by computing the parity for, say, drives 2 and 3: 0+7=7, 9-7=2. 4+3=7, 9-7=2. 6+8=14, rightmost digit is 4, 9-4=5. 2+6=8, 9-8=1. 2+6=8, 9-8=1. 0+9=9, 9-9=0. Sure enough, the first six digits on drive 1 are 225110.
This mutual parity means is that if we lose any one of our drives, we can reconstruct the data that was on it by computing the parity of the other drives. For example, say we lost drive 2. We can replace it and the NAS will rebuild the array:
One final note: I've been showing the parity all on one drive for simplicity, but in a real system, the computed parity isn't stored that way because doing so would lower performance and overwork the parity drive (because its data would have to be updated whenever the data on any other drive was updated). Instead, the parity is spread across all the drives, like this:
This interleaving doesn't affect the failure-resistance of the array. If one drive fails, the NAS can still rebuild it exactly as if all the parity were on a single drive.
Thanks, StephenB. I've edited it to make a couple sentences more clear, and to simplify the parity calculation a little by changing the formula from 10-sum to 9-sum.
@fastfwd & StephenB, I am truly shocked by your shares. I thought I have gracefully closed this thread. I suppose not. Yes, I do know that a NAS should keep track of 'parity.' I just sorta believe that the device and its' f/w just does this 'magic' in real time. I do so appreciate the parity tutorial, but, I'm lost as to how it fits into my thread. I mean no disrespect at all. I learned 'parity' some 40+ years ago at Xerox Corp. The training was 4 days. On the fifth day, the instructor calmly explained the all 'modern' devices I would ever see would do all of my 4 days of calculations just blindingly quick. SO. I quickly forgot about it; but, in nas-speak, I realize it is important still. Fine. I know and accept that parity is required to recreate lost data. That is the magic. And I spent 40+ years recovering 'lost' data with the help of 'parity.' I do so know of its' importance. BTW, I have now re-checked my other NAS and find that both of them are XRAID2. so I have nothing else to do and/or worry about. Now I can re-focus on how to do backups on a ReadyNAS! I do so appreciate both of your shares. Fast FWD, you dragged me back some 40yrs. :rofl: No harm, no foul! The journey was actually fun!
