The solution is to keep a history of backups.
You can store one daily backup, say for the last seven days. Then one backup per week four times per month. This way, if the backup from yesterday had been saved in a bad state, you take the backup from the day before. Or you can take the backup from last week.
To save space you can either use a file system with supports deduplication, use hard links or store only the difference between the backup. Which solution is best, depends on your needs, setup and the software you run.
EDIT: You updated your question and added additional information.
As you already know, you have to separate the data from the backup. A backup is always redundant, if possible even more than one copy. I don't know your NAS solution and their backup software. But I can tell you how I solved this.
I use an old 300MHz system as backup server, which is connected to the file server (that would be your NAS in your configuration). Once per day the backup server switches on and pulls the backup from the file server and writes the data on its own hard drives. As backup software I use rsnapshot. No client computer has access to the backup server in any way. And it is only running for a short time per day.
This is only one possible solution out of many. The key points of a good solution are:
- Keep a history of backups
- A backup is always redundant
- A backup is stored on different hardware (e.g. a second drive, not a second partition on the same drive)
- The client computers must not have access to the backup
- The backup should be as easy as possible, at best fully automatic
- Depending on how often restores are expected, it should not be too big of a burden to restore the data
Best Answer
The solution is still applicable, even if you're using RAID1 instead of
Synology Hybrid RAID(SHR). The only difference if you're using RAID1 is that you'll need to upgrade both drives, and keep them equal in size in order to maximize disk space.As you mentioned you're using a 2-bay system, it won't make any difference anyway; the real benefit of SHR is when you're using 3+ disks, as they can be of different sizes and still minimize the wasted disk space.
Basically the procedure to upgrade a Synology is:
Done!
You still have a copy of your data on the 1TB disks, so if anything goes wrong, you can still recover the data manually. If that happens, it is strongly recommend that you do a full disk copy sector-by-sector (using dd on a Linux machine, or a tool like CloneZilla) before attempting recovery.
Despite the name, the
Synology Hybrid RAIDtechnology is not really proprietary to Synology. It's just some clever use ofMultiple Device(MD) andLogical Volume Manager(LVM2). So if you have an emergency, you can still plug the drives directly to a Linux machine and have fun using md/lvm. Both LVM and MD are open, stable, well documented and widely adopted.