How much storage do I really need?


I have a DroboPro (connected by Firewire to an old iMac running macOS server), it is configured for dual disk redundancy and I have just completed an upgrade of all its original 2TB drives to 3TB drives. Which, according to the calculator, gives me 16.2TB of capacity for data. I have a single 16TB volume on it.

I’m down to about 1.5TB of free space in the volume, and its saying I’m extremely low on space and that I need to replace (at least one) drive with a larger one.

Its being used to do backups of all my other computers, so its going to fill to near capacity before it starts trimming old backups due to space (probably didn’t need to use the default 5 year retention policy…but thought it wouldn’t hurt…but slap a couple of 8 TB drives onto other computers…backup storage disappears fast.)

So what available for data size do I need to actually support a 16TB volume?

Not really wanting to do more drive replacements though, since it was painful enough replacing the original WD Green drives with Enterprise 3TB drives (which I discovered the first 7 are 512 native and the 8th is a 512 emulation…the prices on the drives crept up almost 20% along the way too…)

But, if I have to…is one 4TB drive going to satisfy the DroboPro, or will I need at least 3 more?



I’m confused, and I think my Drobo is too now.

I have/had a DroboPro with 8 x 3TB drives in dual disk redundancy which reported a usable capacity of a bit more than 16TB of storage, for which I have a 16TB HFS volume on it.

Last week I found that one of the drives had failed, not sure why or when the endless flood of email notifications I had gotten the past didn’t happen this time.

But, it was stuck saying that it couldn’t protect me, as I needed at least 2 drives for redundancy or 3 for dual-disk redundancy. Instead of performing data protection to maintain the same level of redundancy over the remaining drives… It was originally 8 x 2TB drives, so I didn’t expect that it be stuck needing 16TB of usable storage to continue to protect me…

I had seen it do such things when a drive failed in my 2nd Gen Drobo, (which had started out with a mix of 1TB, 1.5TB and 2TB drives…initially a 4TB volume to present as 2 x 4TB volumes - one for local time machine backups, and the other for remote (laptop) time machine backups. Using 2 x 2TB and 2 x 4TB drives…)

But, it didn’t want to do anything except demand I give it a new drive to protect the 10.9TB of used storage.

Well, that was until things crashed/froze/etc. last night. (I needed to reboot the computer a couple of days ago, but was resisting trying to figure out why my Drobo wasn’t doing anything…except making access to the volume slow.

After a couple of restarts, to get the volume to reappear, it then went into data protection it appears to be doing single disk redundancy to create a volume that will have 10.96TB of used space, 5.03 TB of free space and 300.92GB of unallocated space for a total of 16.29TB.

ETA 336 hours remaining… meanwhile, its flooding the local screen with “The Drobo is running extremely low on available space…”, “Drobo cannot currently protect your data against hardware…” … oh looks like all the messages were from last week, guess the reboot unblocked it from telling me that it was confused.

Wonder what happens when Amazon delivers a 3TB drive tomorrow… Can, I get it take it and go back to dual disk, or do I have to wait for it finish…or will I never be able to get back to dual disk? The option is greyed out in the dashboard currently.

Wonder if the limit on being able to reduce physical storage behind the 16TB volume is because at one point I did fill it up completely (found I was backing up an 8TB drive on my other computer two different ways…) At current rate, it’ll take a couple of years to get the drobo’s backed up into cloud…as it’s not going any faster on google fiber than it was when I only had 50M/5M cable modem service.



So, as I suspected…replacing the one drive it wanted with a larger disk didn’t satisfy its need for more space as my 16TB volume was more than 80% full, even though the drobo calculator says 8 3TB drives will give me a little bit more than 16TB usable with dual disk redundancy.

But, I replaced the first drive with a 4TB disk, to see what would happen…well, after a week of doing data protection, it tells me that its running low on space and that I need to replace the first disk with a a larger one.

Why do I need something larger than 4TB in slot one, why not continue the sequence like it had when I went from 2TB to 3TB drives. Aside from no explanation yet on why 8 - 3TB drives wasn’t enough. Not sure if 6TB drives will be next.

Though for the 4TB’s I’m using coolspin drives. My pre-drobo array used 2TB ones, and…its probably been close to 10 years now, with more than half of them still in production, had some die after a recent move (horrible movers…at last I was able to retrieve them after they threw them out.)

Anyways…I ignored its suggesting that I replace the 4TB drive with something larger and replace (instead of replace one of 7 - 3TB drives with something larger…) And, swap another 4TB drive in for a 3TB one. After thinking about it for a while, it changed the light on the first slot to red, and demanded I replace that with a bigger drive in order for it to be able to protect my data.

Yet, as I had seen before, it showed the newly replaced drive as 4TB, and green (but there’s nothing on it yet…) The fact that I don’t have anything larger than 4TB free at the moment, I’m ignoring its demand…since it took nearly a month to do data protection when I had upgraded two drives at the same time because that’s what it had demanded. But, the last time I did that…it took a few hours but eventually it accepted its fate and went to work with growing with just the one drive upgraded.

I was starting to work on opening a ticket when I changed its mind and went to work…only its typical week each time.

Hopefully, my DroboPro will come to its senses by morning and then we’ll repeat this mess when I grow to 3 - 4TB drives + 5 - 3TB drives to support 16TB. They need to update the drobo calculator.

This is making me question whether I want to see if I can get a Drobo 8D to work with Thunderbolt 1.

Or perhaps a NAS/iSCSI solution is what I could look at…since I have a dual 1Gbps fiber core home network (hmmm, that’s what we had at work until it was upgraded to a dual 10Gbps fiber core…and to think that’s already slow…since that’s only catching it up to our WAN…

It didn’t have to be fiber, but was joking about it in another forum…and, decided it’d be cool and cheaper than shielded CAT6 or CAT7. I liked the CAT7, because it used flat cables… Though they do make it a bit of a challenge on which way to keep the cable flat when arching up to feed the bottom row of switch, or arching down to feed the upper row… :wink: Didn’t help as much as I thought keeping things labeled…

The Dreamer.