In most Synology home user installations, we use SHR instead of the traditional RAID, and we are often asked what it is, how it differs from the traditional RAID, and if there are any drawbacks to using it.
What is Synology SHR - Synology Hybrid RAID
Synology SHR is a RAID, which allows you to mix hard drives with different capacities. Let us take a quick look at RAID ( the classic RAID) first before we look at SHR.
RAID is a way to combine multiple hard drives so that they look like a single hard drive. So if you have 5 disks, you can combine them all to logically look like a single disk, which is easier to manage (compared to 5 individual volumes) and also gives you protection against disk failures.
If you have RAID 5, you are protected against ANY 1 disk failure, if you have RAID 6, you are protected such that even ANY 2 disks in the array can fail without affecting your DATA.
The classic RAID is a staple in NAS because you always have multiple disks in a NAS and you always want to connect them logically. But RAIDs are not without their problems. One of the problems is that you need to use drives with the same capacity in a RAID. For example, if you use 6 and 8TB drives in one RAID, all the drives will be reduced to the smallest size, i.e. 6TB in this case.
SHR solves this problem for you. With SHR you can mix drives with different capacities and it will digitally partition these drives to the smallest drive and then create a conventional RAID. You will not lose any drive capacity when you use SHR. This is the most important reason for using SHR - you can mix drives with different capacities in one RAID without wasting space.
How Synology SHR differs from traditional RAID
Synology SHR allows you to mix drives with different capacities in one RAID without losing capacity, which is not possible with the classic RAID. This is the major difference.
Also SHR levels are simpler to chose - there are only 2 SHR 1 and SHR 2, while in Classic RAID you have many other levels.
SHR splits your large drive into many smaller drives first , and then applies RAID logic to combine them. Traditional RAID doesn't do that.
What is the advantage of Synology SHR
The only advantage is of course the possibility to mix drives of different sizes without wasting space. But this advantage alone is usually all you need to choose SHR over the traditional RAID in home setup.
What are the disadvantages of Synology SHR
None that we know of.
You may have read that SHR is a proprietary technology from Synology and that it is better to use the traditional RAID if you ever need to use this RAID from Synology - that is not true.
First - SHR is not a Synology proprietary technology , it works with Linux LVM and can be assembled out of a Synology box also.
Second - it is highly unlikely that you will need to compile RAID from the Synology box. You would only do it if your data is lost and you contact a data recovery company. For them, putting together a hybrid RAID is no different than the classic RAID.
The third argument we often hear is that you can not port the drives to a QNAP box. Well, even with Classic RAID you can not move the drives between different vendors NAS boxes without losing your data.
How is SHR1 different from SHR2. Which one should you choose
SHR1 is similar to RAID 5 from Classic RAID, it can tolerate ANY 1 disk failure because there is a calculated parity that you can use to reconstruct your data.
SHR 2 is similar to RAID 6 from Classic RAID with 2 parity bits. It can survive ANY 2 disk failures.
Choose SHR2 if you can. It has the maximum hardware failure protection. If you need more space, go with SHR1 as it has 1 HDD failure protection so it gives you more space.
In the latest version of DSM, you can migrate from SHR1 to SHR2 to maximize redundancy. It means you can start with SHR1 and later as your hard drives start to age, you can shift to SHR2.
