Need redundant Time Machine backup solution for iMac with 4TB of external data

Greetings all, I have an iMac with a 4TB drive full of photos that is not currently backup up.  Yes, I know I am being stupid here. I also had documents and spreadsheets that need to be backed up on the 500GB drive on the iMac.  I am looking for a backup solutuion that will handle these data needs.  I have investigated a Synology DS215J unit with 2 6TB drives inside that could be setup just for Time machine backups with RAID 1 protection, but is that enough space?  I thought I read somewhere that a RAID 1 configuration on this unit could have a max size of 6TB and I am not sure that would be enough space to handle time machine backups without problems.  Then I thought that I could use the Synology DS215J with 2 6TB drives as the external HD for my photos and then use Time machine to back up to another 6TB drive?  I am a bit confused on what to do here but I am hoping you can help me figure out a simple solution that is not too expensive.  Thank you for any input.  Marc
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Thomas Zucker-ScharffSolution GuideCommented:
Yes you should use TM, but I am not a MAC expert and cannot advise you there.  What I will say is that you should have a cloud backup as well.  My feeling has always run with the notion that "If it isn't backed up in at least two OTHER places, than it isn't important."  Check out this page for the Backup "Rule of 3." Also investigate cloud backup solutions.  I highly recommend Crashplan for several reasons, check them out here.
You are confusing backup with archiving.  Let's say for the sake of argument that you have a redundant backup solution already.   ... Then there is a software bug, fire, flood, or you just type in something stupid and wipe it out.

1) So do yourself a favor and get an internet based backup solution to handle offsite backup.  Personally i use the iDrive product on all my mac's and iPhones.   It backs up as little or as much as you want and you can control how much bandwidth it uses and scheduling.  Price is fair.  Then just buy a 4TB USB3 attached HDD for local copies.
Time Machine does snapshots and 6 TB may be enough, depending on how often your data changes and how much data you have.

If you have 4 TB of data and  5% of the data changes and 95% of the data remains unchanged, you should be able to keep about  101 snapshots on the 2 extra TB of space.

If 25%(1TB) of your 4TB is constantly changing and 75% (3TB)remains unchanged, then you would only be able to keep 3 snapshots on your 6 TB of space.

If you have 4 TB of constantly changing data and want to keep off site backups for that much data, cloud is a bit expensive and quite slow, even if you have 100 MB internet.  It would be easier to get a single drive and back the unchanging data to it and have a service, like Iron Mountain, to come once a week to take your data off site.  You could have them take multiple weeks of data to store off site.

It really depends on how many changes you wish to keep and what sort of backup you are looking for and how much data is permanent and how much is changing.
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nappy_dThere are a 1000 ways to skin the technology cat.Commented:
My suggestion but there is no such solution as cheap when it comes to high data volumes for backup and redundancy for RAID.

In any even, my solution is based on what I currently do:
Install a QNAP NAS TS420 is the version I have.  It supports the time machine protocal and you can also create AFP file shares
QNAP also has a plugin that allows you to sync backups to a cloud backup solution.  You can consider this a backup to your backup and RAID redundancy. iDrive
Thomas Zucker-ScharffSolution GuideCommented:

If anyone is interested here are the definitions.

According to SNIA’s online dictionary, the terms are defined as follows:
Backup: A collection of data stored on (usually removable) non-volatile storage media for purposes of recovery in case the original copy of data is lost or becomes inaccessible; also called a backup copy.
Archive: A collection of data objects, perhaps with associated metadata, in a storage system whose primary purpose is the long-term preservation and retention of that data.

From blog (read more from this blog)
Backup – When backing up your data, you are protecting both active and inactive information which encompasses all of your production data.  As part of the process, you are copying your vital information to a backup target such as disk or tape.  It is critical to recognize that a backup is a copy of production information and the actual data still resides on the production storage systems.  Thus, if your backup system suffers a catastrophic data loss, your operations could still continue normally since your production data would not be impacted; however, you would be operating at an elevated risk.
Archive – Archive solutions solve a different problem.  These technologies are typically used to maintain older or inactive data for extended periods of time.  Archive systems typically move older or inactive information off of primary storage to dedicated systems which are optimized for low cost long-term storage.  A key differentiator from backup is that the data stored in an archive is actual production data and hence a loss of an archive system will result in permanent loss of production information. (To be fair, the information will likely be older and less active, but unlike backup, it is the only copy of the data.)

I would just point to my article on backup, but it hasn't been accepted yet.

Cloud/offsite/versioning backup is a necessity.
@Thomas Zucker-Scharff
Respectfully, you are just using arbitrary definitions for backup and archiving.  Archiving is not necessarily the "only copy of the data". Certainly you can't make the case that having the only copy of your data offline, but at the same site satisfies as an archive.

My point is that for something like photos, you need both a local copy of at least some of the ones you enjoy watching, or plan on watching any time soon, and an offsite protected, redundant copy in case of a natural or human disaster that can wipe out everything you have locally.

I spend less than $100 annually with iDrive for a  few TB worth of RAID-protected, redundant, offsite, 24x7x365 available copies of data I do not want to lose.   I also have live copies, as well as a Solaris / ZFS-based appliance that emulates an apple time machine via AFP.    I can sleep at night, and my suggesting to just get a local USB-attached drive to make an offline local copy and perhaps a few hundred dollars a year to get 4+ TB for archiving purposes is not only sound, but is frugal.

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A backup is a duplicate of the data.  You can have a backup onto a RAID, but just using RAID, by itself, is not backup.  RAID is for maintaining uptime and for larger storage volumes and for data access speed.  You need to have a copy of your data elsewhere to have a backup.

You can also just put a personal disk in a bank safe deposit box for much less money than "cloud" storage.  If you already have a bank safe deposit box, you're not spending too much extra.  It's good to keep multiple copies of data, so if you wish to use cloud storage as well as a separate disk to put into a safe deposit box, you'll have additional redundancy.  Don't rely on just one source of backups or archives if you have critical information that you must save.  How much is the data worth to you?  That determines how much redundancy you should have.

As with all backups and archives, you must periodically verify that the data exists.  I've encountered numerous organizations that have backed up data with their back up solutions, but never, ever verified the data, only to find that the data wasn't actually ever backed up.  Data was lost because their backup process was flawed.  Archived data should also be checked and moved onto new media periodically, if you really want to keep that data.
A backup in a safety deposit box is a bad idea.  100% of disk drives fail .. eventually.    It is inevitable that the disk in the safety deposit box will lose all or part of the data.

An offsite copy with a 3rd party company that keeps the data online in a RAID array (with their own backups) is the safe and permanent way to retain data.
You don't keep the backup in the safe deposit box forever.  It's an offsite storage for the disk that gets rotated out every day, week or month depending on data storage needs.  You would have multiple cheap disks to rotate out.  You may keep several weeks worth of data.  This is just a "poor man's" version of Iron Mountain storage facilities.  As with all backups, you must always verify the data periodically.  If you're just storing the disk in a safe deposit box permanently, you're doing it wrong.  There are different levels and needs for backups.  Backups do not have to be online 24/7 on a RAID.  Not everyone needs 24/7 backups or has the money to spend on them.
I would also suggest that a 2 disk external RAID is a waste of money.  Get 3 separate 6 GB disks and you rsync them, and you'd have a better back solution that you can even take to a safe deposit box and swap each week.  You could also get a 6 TB disk for time machine and then 2 much cheaper 4 TB disks and just rsync a copy of the iMac.

RAID is for uptime availabitily, data speed and larger storage space.  If you're storing to RAID, you should go with 4 disks or more to benefit from all 3 criteria, but you'll still want to get another backup.   2 disks RAID mirrors are great for servers that must remain up, but only if you have someone around to swap out that failed disk before the other one fails and the only criteria you satisfy is the uptime availability.  If you don't need 24/7 uptime, you don't really need the 2 disk RAID.  The 2 disk units don't buy you extra backup, because it's not a backup, it's a mirror.  Both disks are on the same RAID controller and the same chassis in the same physical location.  They also only buy you a marginally better reliability in the home or small office use case because you don't have dedicated sys admins waiting around to swap disks the moment one fails.  If you're just using it as a backup device, it's not ideally cost effective.
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