Spanned Volume - How disk writes are performed
How would having a spanned volume help or hurt me in this scenario? I have 4 physicial disks comprised of 4 distinct volumes:
Disk 1, Volume 1 = system (250GB)
Disk 2, Volume 2 = data (2TB)
Disk 3, Volume 3 = backup (2TB)
Disk 4, Volume 4 = backup (2TB)
If I were to convert Disk 3 and Disk 4 to dynamic disks and span volume 3 across both, how will my backup data be written to that 4TB spanned volume? Does data get written to Disk 3 in the volume until it is full, then continue to Disk 4 in the same volume OR does data get written to either disk at random? My ultimate question or concern is that if I lose one physical disk in the spanned volume, what backup data will I be left with (if any)?
Disk 1, Volume 1 = system (250GB)
Disk 2, Volume 2 = data (2TB)
Disk 3, Volume 3 = backup (2TB)
Disk 4, Volume 4 = backup (2TB)
If I were to convert Disk 3 and Disk 4 to dynamic disks and span volume 3 across both, how will my backup data be written to that 4TB spanned volume? Does data get written to Disk 3 in the volume until it is full, then continue to Disk 4 in the same volume OR does data get written to either disk at random? My ultimate question or concern is that if I lose one physical disk in the spanned volume, what backup data will I be left with (if any)?
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ASKER
I'm in agreement. As per the hyperlink you provided... "Why, then, would anyone use spanning? Because they have hardware RAID to provide the redundancy. This combination offers the best of both worlds—redundancy provided by the hardware RAID controller and flexibility to expand volumes as needed, using Disk Management. Yet another compelling argument for hardware RAID, in case you needed any more."
The suggestion is that you can mirror a spanned volume, perhaps to a singular disk that has equal or greater storage capacity. Like you, I have no experience with this and can only suppose that the rationale for a spanned volume is what you suppose, an emergency/temp fix or a temporal solution.
The suggestion is that you can mirror a spanned volume, perhaps to a singular disk that has equal or greater storage capacity. Like you, I have no experience with this and can only suppose that the rationale for a spanned volume is what you suppose, an emergency/temp fix or a temporal solution.
Why ever use it? Simply to provide a larger volume than a single disk supports, but ONLY if you have good backups.
I never used them until recently (last year) when drive capacities became so large that I could store my media collection on a "single" volume in my main PC. I created a 16GB volume with 4 4TB disks; and have a backup utility run every night that turns on my backup server; syncs the backup; and then shuts down the server. Previously I ran the server 24/7 ... now it's on for just a few minutes/day. I would NOT use spanned volumes if you do not have a complete backup, however. With a full backup, a failed disk means you need to (a) replace the failed disk; (b) recreate the spanned volume across all of the disks involved; and then (c) copy the entire backup to the spanned volume. Clearly that's a LONG copy process if you have many TB's of data.
I never used them until recently (last year) when drive capacities became so large that I could store my media collection on a "single" volume in my main PC. I created a 16GB volume with 4 4TB disks; and have a backup utility run every night that turns on my backup server; syncs the backup; and then shuts down the server. Previously I ran the server 24/7 ... now it's on for just a few minutes/day. I would NOT use spanned volumes if you do not have a complete backup, however. With a full backup, a failed disk means you need to (a) replace the failed disk; (b) recreate the spanned volume across all of the disks involved; and then (c) copy the entire backup to the spanned volume. Clearly that's a LONG copy process if you have many TB's of data.
ASKER
Agreed. If you have a spanned volume, you need a backup of it. The scenario I described would mean using the spanned volume to backup the system and data volumes combined to a targeted spanned volume. In practice, using a spanned volume as a destination for backups is a piss-poor idea. Using them as a source for backup is a different story.
I enjoy this kind of discussion. I thank you both for being as engaging as you have been. I'm still a bit curious about using them in a RAID 1 scenario (as the source volume), but I've not found any documentation to support that notion. If either one of you do, please post.
I enjoy this kind of discussion. I thank you both for being as engaging as you have been. I'm still a bit curious about using them in a RAID 1 scenario (as the source volume), but I've not found any documentation to support that notion. If either one of you do, please post.
Windows does support replacing failed volumes if you're using dynamic disks with either mirrored (RAID-1) or RAID-5 volumes. But only the server OS's support RAID-5.
It's a shame Windows 7 (and 8) don't support RAID-5 volumes with dynamic disks. There's no technical reason they don't ... the capability is simply "crippled" to distinguish them from the server OS's. [There are actually instructions you can find to enable this capability on the desktop OS's, but I do NOT recommend doing this -- you'd potentially be one Windows Update away from losing all your data !!]
It's a shame Windows 7 (and 8) don't support RAID-5 volumes with dynamic disks. There's no technical reason they don't ... the capability is simply "crippled" to distinguish them from the server OS's. [There are actually instructions you can find to enable this capability on the desktop OS's, but I do NOT recommend doing this -- you'd potentially be one Windows Update away from losing all your data !!]
Good that you have worked out why not to use spanned or striped disks in your situation but they were occasionally needed in the past when there was a 2TB limit on what Windows saw as disks. With large external RAID systems it was sometimes necessary to slice the array into several sub-2TB logical disks, present all of these slices to Windows and then stitch them together using dynamic disks. In these situations you could still lose a physical disk and keep going due to the underlying RAID on the external unit. Fortunately the 2TB barrier has now gone in most situations so such a bodge is no longer required.
ASKER
I expanded significantly on the response of the two that helped me. I think that it is important for others seeking an answer to this question in the future to read the the full solution. I awarded all of the points to both of the respondents.
I have never personally thought using this was a good option, so never had first-hand experience using or supporting it, but I once saw this on a Microsoft certification prep exam, where the answer was, in order to add space to a disk that was running low, to "span" to another disk. I don't know how Microsoft figures this is a good feature, unless it was intended only to be an emergency/temporary fix, OR it is simply a lingering relic feature of a different time in computing when it might have been considered "adaptive" and "forward-thinking" for the time and options that were then-available.