I have a home server.

Initially conceived and sized so I could digitize my (rather sizeable) DVD collection, I started using it for other things; I added a few play VMs on it, started using it as a destination for the deja-dup-based backups of my laptop and the time machine-based ones of the various macs in the house, and used it as the primary location of all the photos I've taken with my cameras over the years (currently taking up somewhere around 500G) as well as those that were taking at our wedding (another 100G). To add to that, I've copied the data that my wife had on various older laptops and external hard drives onto this home server as well, so that we don't lose the data should something happen to one or more of these bits of older hardware.

Needless to say, the server was running full, so a few months ago I replaced the 4x2T hard drives that I originally put in the server with 4x6T ones, and there was much rejoicing.

But then I started considering what I was doing. Originally, the intent was for the server to contain DVD rips of my collection; if I were to lose the server, I could always re-rip the collection and recover that way (unless something happened that caused me to lose both at the same time, of course, but I consider that sufficiently unlikely that I don't want to worry about it). Much of the new data on the server, however, cannot be recovered like that; if the server dies, I lose my photos forever, with no way of recovering them. Obviously that can't be okay.

So I started looking at options to create backups of my data, preferably in ways that make it easily doable for me to automate the backups -- because backups that have to be initiated are backups that will be forgotten, and backups that are forgotten are backups that don't exist. So let's not try that.

When I was still self-employed in Belgium and running a consultancy business, I sold a number of lower-end tape libraries for which I then configured bacula, and I preferred a solution that would be similar to that without costing an arm and a leg. I did have a look at a few second-hand tape libraries, but even second hand these are still way outside what I can budget for this kind of thing, so that was out too.

After looking at a few solutions that seemed very hackish and would require quite a bit of handholding (which I don't think is a good idea), I remembered that a few years ago, I had a look at the Amazon Storage Gateway for a customer. This gateway provides a virtual tape library with 10 drives and 3200 slots (half of which are import/export slots) over iSCSI. The idea is that you install the VM on a local machine, you connect it to your Amazon account, you connect your backup software to it over iSCSI, and then it syncs the data that you write to Amazon S3, with the ability to archive data to S3 Glacier or S3 Glacier Deep Archive. I didn't end up using it at the time because it required a VMWare virtualization infrastructure (which I'm not interested in), but I found out that these days, they also provide VM images for Linux KVM-based virtual machines (amongst others), so that changes things significantly.

After making a few calculations, I figured out that for the amount of data that I would need to back up, I would require a monthly budget of somewhere between 10 and 20 USD if the bulk of the data would be on S3 Glacier Deep Archive. This is well within my means, so I gave it a try.

The VM's technical requirements state that you need to assign four vCPUs and 16GiB of RAM, which just so happens to be the exact amount of RAM and CPU that my physical home server has. Obviously we can't do that. I tried getting away with 4GiB and 2 vCPUs, but that didn't work; the backup failed out after about 500G out of 2T had been written, due to the VM running out of resources. On the VM's console I found complaints that it required more memory, and I saw it mention something in the vicinity of 7GiB instead, so I decided to try again, this time with 8GiB of RAM rather than 4. This worked, and the backup was successful.

As far as bacula is concerned, the tape library is just a (very big...) normal tape library, and I got data throughput of about 30M/s while the VM's upload buffer hadn't run full yet, with things slowing down to pretty much my Internet line speed when it had. With those speeds, Bacula finished the backup successfully in "1 day 6 hours 43 mins 45 secs", although the storage gateway was still uploading things to S3 Glacier for a few hours after that.

All in all, this seems like a viable backup solution for large(r) amounts of data, although I haven't yet tried to perform a restore.

In my previous post, I explained how I recently set up backups for my home server to be synced using Amazon's services. I received a (correct) comment on that by Iustin Pop which pointed out that while it is reasonably cheap to upload data into Amazon's offering, the reverse -- extracting data -- is not as cheap.

He is right, in that extracting data from S3 Glacier Deep Archive costs over an order of magnitude more than it costs to store it there on a monthly basis -- in my case, I expect to have to pay somewhere in the vicinity of 300-400 USD for a full restore. However, I do not consider this to be a major problem, as these backups are only to fulfill the rarer of the two types of backups cases.

There are two reasons why you should have backups.

The first is the most common one: "oops, I shouldn't have deleted that file". This happens reasonably often; people will occasionally delete or edit a file that they did not mean to, and then they will want to recover their data. At my first job, a significant part of my job was to handle recovery requests from users who had accidentally deleted a file that they still needed.

Ideally, backups to handle this type of situation are easily accessible to end users, and are performed reasonably frequently. A system that automatically creates and deletes filesystem snapshots (such as the zfsnap script for ZFS snapshots, which I use on my server) works well. The crucial bit here is to ensure that it is easier to copy an older version of a file than it is to start again from scratch -- if a user must file a support request that may or may not be answered within a day or so, it is likely they will not do so for a file they were working on for only half a day, which means they lose half a day of work in such a case. If, on the other hand, they can just go into the snapshots directory themselves and it takes them all of two minutes to copy their file, then they will also do that for files they only created half an hour ago, so they don't even lose half an hour of work and can get right back to it. This means that backup strategies to mitigate the "oops I lost a file" case ideally do not involve off-site file storage, and instead are performed online.

The second case is the much rarer one, but (when required) has the much bigger impact: "oops the building burned down". Variants of this can involve things like lightning strikes, thieves, earth quakes, and the like; in all cases, the point is that you want to be able to recover all your files, even if every piece of equipment you own is no longer usable.

That being the case, you will first need to replace that equipment, which is not going to be cheap, and it is also not going to be an overnight thing. In order to still be useful after you lost all your equipment, they must also be stored off-site, and should preferably be offline backups, too. Since replacing your equipment is going to cost you time and money, it's fine if restoring the backups is going to take a while -- you can't really restore from backup any time soon anyway. And since you will lose a number of days of content that you can't create when you can only fall back on your off-site backups, it's fine if you also lose a few days of content that you will have to re-create.

All in all, the two types of backups have opposing requirements: "oops I lost a file" backups should be performed often and should be easily available; "oops I lost my building" backups should not be easily available, and are ideally done less often, so you don't pay a high amount of money for storage of your off-sites.

In my opinion, if you have good "lost my file" backups, then it's also fine if the recovery of your backups are a bit more expensive. You don't expect to have to ever pay for these; you may end up with a situation where you don't have a choice, and then you'll be happy that the choice is there, but as long as you can reasonably pay for the worst case scenario of a full restore, it's not a case you should be worried about much.

As such, and given that a full restore from Amazon Storage Gateway is going to be somewhere between 300 and 400 USD for my case -- a price I can afford, although it's not something I want to pay every day -- I don't think it's a major issue that extracting data is significantly more expensive than uploading data.

But of course, this is something everyone should consider for themselves...