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Forum Discussion
WD Compatibility
Two questions: 1. I have two WD Elements and one WD My Book. I did a brief search for compatibile drives with the 104 and only came up with about three for WD. Is that right or was I looking i...
LDG wrote:
Xraid sounds much better...pretty much what I do anyway, actually. The downside is finding a way to keep the the first disks connected. I simply like having constant access to everything. Xraid allows for expansion the way I would like it to, but then I still have two disks that I'd like to continue to be accessible.
There might be still be some confusion here on what RAID actually does. XRAID creates a single volume (think of it as a "virtual disk") from the physical disks you have installed. By default the NAS calls this volume "data".
All your data is on this virtual disk, and you expand it by replacing the physical disks with larger sizes. All the data remains accessible when you expand - nothing is destroyed (unless something goes wrong).
Also, if a single disk in the volume fails, the volume is "degraded". But you still have all your data available. You pop in a new disk (either the same size, or matching the size of the largest disk in the array), and the redundancy is restored.
This doesn't keep your data completely safe (so you still need a backup). But it does keep everything available through routine disk replacements.
So with XRAID it actually doesn't make sense to say "I still have two disks that I'd like to continue to be accessible.", since the disks are all combined into the virtual disk.
StephenB wrote:
LDG wrote:Xraid sounds much better...pretty much what I do anyway, actually. The downside is finding a way to keep the the first disks connected. I simply like having constant access to everything. Xraid allows for expansion the way I would like it to, but then I still have two disks that I'd like to continue to be accessible.
There might be still be some confusion here on what RAID actually does. XRAID creates a single volume (think of it as a "virtual disk") from the physical disks you have installed. By default the NAS calls this volume "data".
All your data is on this virtual disk, and you expand it by replacing the physical disks with larger sizes. All the data remains accessible when you expand - nothing is destroyed (unless something goes wrong).
Also, if a single disk in the volume fails, the volume is "degraded". But you still have all your data available. You pop in a new disk (either the same size, or matching the size of the largest disk in the array), and the redundancy is restored.
This doesn't keep your data completely safe (so you still need a backup). But it does keep everything available through routine disk replacements.
So with XRAID it actually doesn't make sense to say "I still have two disks that I'd like to continue to be accessible.", since the disks are all combined into the virtual disk.
So if Drive A and B are in there and full, I can take them out and put same size or larger C and D drives in. Does the data from A and B stay on the virtual disk while I can add to C and D? Or do C and D need to be larger to accomodate the virtual data? Would the physical drives then act as back up?
I feel like I've drawn a false conclusion that a NAS can support virtual data itself, but that would mean they have their own internal storage and I didn't think diskless ones did.
You're right! I am confused! (maybe)
The "virtual disk" is built on top of the physical disks - so that all the storage is still on the physical disks.
For example, if you have four 3 TB disks installed, you have 12 TB of total storage. The NAS will create a 9 TB virtual disk. The remaining 3 TB is used to create redundancy - allowing all the data to saved on the 9 TB virtual disk to remain available even if one of the 3 TB disks fails or is removed.
This virtual disk looks like a single 9 TB drive to you. Also, your data is spread across all 4 physical disks. For instance, if you have a 4 GB movie, part of it is on disk 1, part on disk 2, etc. It still is one file, but it is saved across all the disks.
LDG wrote:
So if Drive A and B are in there and full, I can take them out and put same size or larger C and D drives in.
Again, it is meaningless to say Drive A is full. The virtual disk volume is what becomes full. The files are spread across all the physical drives.
When it does get full, you can replace the physical drives with larger ones (one at a time). So if you changed two of the 3 TB drives with 6 TB drives, the NAS would expand the virtual disk from 9 TB to 12 TB. The space needed for redundancy would also grow - in this example from 3 TB to 6 TB. The virtual disk then looks like a single 12 TB drive to you, with no data loss.
The rule for capacity is that volume size is the sum of all the disks minus the largest disk. The amount needed for redundancy is equal to the largest disk.
When you replace a physical disk, you either use a disk of the same size as the one you are removing, or you add a disk that is >= the largest disk in the array.
StephenB wrote:The "virtual disk" is built on top of the physical disks - so that all the storage is still on the physical disks.
For example, if you have four 3 TB disks installed, you have 12 TB of total storage. The NAS will create a 9 TB virtual disk. The remaining 3 TB is used to create redundancy - allowing all the data to saved on the 9 TB virtual disk to remain available even if one of the 3 TB disks fails or is removed.
This virtual disk looks like a single 9 TB drive to you. Also, your data is spread across all 4 physical disks. For instance, if you have a 4 GB movie, part of it is on disk 1, part on disk 2, etc. It still is one file, but it is saved across all the disks.
LDG wrote:So if Drive A and B are in there and full, I can take them out and put same size or larger C and D drives in.
Again, it is meaningless to say Drive A is full. The virtual disk volume is what becomes full. The files are spread across all the physical drives.
When it does get full, you can replace the physical drives with larger ones (one at a time). So if you changed two of the 3 TB drives with 6 TB drives, the NAS would expand the virtual disk from 9 TB to 12 TB. The space needed for redundancy would also grow - in this example from 3 TB to 6 TB. The virtual disk then looks like a single 12 TB drive to you, with no data loss.
The rule for capacity is that volume size is the sum of all the disks minus the largest disk. The amount needed for redundancy is equal to the largest disk.
When you replace a physical disk, you either use a disk of the same size as the one you are removing, or you add a disk that is >= the largest disk in the array.
Alright, I think I'm understanding...I'm just used to filling up a 1 Tb HD and then moving on to the next 1 TB. That doesn't seem to be a viable option here. I'm guessing replacing one physical disk with another of the same size really does nothing? The info would all be on the virtual disk and once the new one is in, it would just be filled immediatelly.
LDG wrote:
I'm just used to filling up a 1 Tb HD and then moving on to the next 1 TB...
This approach is different from that, and aims to keep all your data available on-line. You don't have to use XRAID, but even if you use JBOD (one disk per volume) the NAS still isn't designed to let you add/remove internal drives like they are books on a library shelf (as you are doing with USB drives now). One aspect is that the SATA connector used by internal drives isn't designed for a lot of insertions/removal.
...I'm guessing replacing one physical disk with another of the same size really does nothing? The info would all be on the virtual disk and once the new one is in, it would just be filled immediatelly.Yes. When you replace a disk with a new one of the same size, then what happens is that NAS reconstructs the contents of the old disk and writes it to the new one. It uses the redundancy data (combined with the actual data) on the other physical disk drives to do that. That is called "resyncing". While this is happening, you can still access all the data (the NAS will simply this reconstruction on the fly). Performance is reduced, but the data is all there.
You'd do that replacement when the original disk fails.
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