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The backup volume
08-18-2016, 11:12 PM
Post: #1
The backup volume
I have some questions on the backup volume that aren't answered on the info web page.

Does the backup volume actually reserve drive space? That is, if I fill the primary partition to the point of it needing more/larger drives, does that also use up all the available space in the backup volume?

And if it does, and I have more than one volume, how does it split the allocation between the standard volumes?
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08-19-2016, 10:02 AM (This post was last modified: 08-19-2016 10:26 AM by Paul.)
Post: #2
RE: The backup volume
hi sandshark, you may have been looking at this same page?
https://myproducts.drobo.com/article/AA-01809

though there, it mentions this:
"The size of this volume can be limited to a fixed size in order to limit how much space can the backup application use."

am not 100% sure, but i think it would be fixed (and reserved) in order to be a reliable amount of free space that can be planned for in backups, but please hang in there in case more info is found or from others who may have used it too to play safe....
i just saw this page as well, and it sounds like a dedicated reserved area based on this:
https://myproducts.drobo.com/article/AA-01862

(btw i have XP home SP2, a Drobo v1 with 2x 1TB/2x 1.5TB WD greens, & a bkp Drobo v2 with the same + a DroboShare: unused)
& a DroboS v2 with 3xWD15EADS &2x1TB in DDR mode on win7, & a drobo5D (all usb)
  • btw i did a sustained (write) operation for about 6 hours, and got 13.2MB / sec ...objection? "sustained" :)
    (16.7MB/s on a v2 & 47-96MB/s drobo-s)
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08-21-2016, 08:42 PM
Post: #3
RE: The backup volume
Yes, that is what one would expect "dedicated" and "fixed" to mean, but apparently those help pages were written in a different English than what I was brought up speaking. I took out my 6TB drives and put in two 1TB ones to make it easier to fill up, and what I found is that the backup volume is nothing more than an extra volume for which you can specify the size. If the main volume(s) fill up the available drive space, you will have no real space for the backup until you add/replace drives, but the Drobo will still report to the OS that there is plenty of space left. So, your backup will fail (or retry forever, depending on how it was programmed) and the software will not know that it needs to delete files to make space.

So, in order to make your backup software work properly with this partition, you have to be sure it fills the backup volume before you run out of real drive space or be prepared to add/replace drives if it needs more real space. So, chosing the right size is extremely important.

With this behavior, the second question is moot. It doesn't actually reserve any space, so it doesn't take it away from anything.

All volumes on the Drobo, the Backup one included, are dynamic virtual volumes -- they do not (necessarily) represent real drive space and all compete for the same real drive space. If you put 4 6TB drives in a Gen3, it will create two 16TB volumes. And each will use up additional space on the drives until its 16TB volume limit is reached or you run out of real drive space. Adding a Backup partition simply adds an additional volume to the competition. The only difference is that you can specify the maximum size it will reach, where any other partition is automatically 16TB. It's going to help with backups, but it certainly doesn't take care of all issues and it creates some on its own.

Given this behavior, I believe the better option may be to create a fixed size Windows virtual hard disk within a Drobo volume, the Backup one or another. While it will subtract from the remaining space in the volume, it will reserve that space up front. Note that a dynamic virtual disk won't do the same, and the Drobo docs specifically say it does not support dynamic disks created in one of it's volumes (a dynamic virtual drive on a dynamic virtual volume does sound like a recipe for disaster). I'm going to experiment a bit with this option.

This is how the Backup Volume behaves when formatted as NTFS and used with Windows. Mac mileage may vary (though I rather doubt it).
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08-22-2016, 01:39 PM (This post was last modified: 08-22-2016 01:41 PM by Paul.)
Post: #4
RE: The backup volume
thanks for posting information about how things were for you on the windows side. (i think it's very good info to know, even if you essentially had to answer your own question) Smile

there are probably some pros and cons to the way it worked. (possibly a design choice pro, was that the overall drobo would still have lots of free space, and still perform fairly quickly, right up to when the data on the overall drobo starts reaching the 2 main stages of around 85% and 95% full - whereas if 50% of it was already allocated with a fixed virtual file, for example, then you could only have about 35% of space to use up, before reaching the 1st known performance line)

but you are right, there can be lots of hassles if they compete for the same space and if a new user has not taken things into consideration.

i havent had much use of dynamic virtual files (i think on mac its a sparse bundle) but i have used a large i think 10GB virtual file on a drobo, to hold my very own virtual cddb and that worked great. (essentially, i had some net access problems from time to time and end up choosing to dowload the whole cddb - but since it is made up of about 1 million tiny text files, i didnt want those clogging up the drobo filesystem itself, and also didnt necessarily want to have those included in my "cathy" search catalogue database of my drobo) Smile

(btw i have XP home SP2, a Drobo v1 with 2x 1TB/2x 1.5TB WD greens, & a bkp Drobo v2 with the same + a DroboShare: unused)
& a DroboS v2 with 3xWD15EADS &2x1TB in DDR mode on win7, & a drobo5D (all usb)
  • btw i did a sustained (write) operation for about 6 hours, and got 13.2MB / sec ...objection? "sustained" :)
    (16.7MB/s on a v2 & 47-96MB/s drobo-s)
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10-24-2016, 03:34 PM
Post: #5
RE: The backup volume
(just linking to your latest thread)
http://www.drobospace.com/forums/showthr...http://www.drobospace.com/forums/showthread.php?

(btw i have XP home SP2, a Drobo v1 with 2x 1TB/2x 1.5TB WD greens, & a bkp Drobo v2 with the same + a DroboShare: unused)
& a DroboS v2 with 3xWD15EADS &2x1TB in DDR mode on win7, & a drobo5D (all usb)
  • btw i did a sustained (write) operation for about 6 hours, and got 13.2MB / sec ...objection? "sustained" :)
    (16.7MB/s on a v2 & 47-96MB/s drobo-s)
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