When building a NAS you have to ask yourself a tough question, HDDs or SSDs? HDDs have now been completely replaced in PCs and notebooks, and for good reason. #
SSDs are faster, use significantly less power, make no noise and are often more “predictable” when it comes to failures.
However, they still have one major disadvantage: the price. Anything over 4 TB is practically unaffordable and SSD prices are currently rising again anyway.
QNAP offers an exciting feature on its NAS systems, QTier. QTier allows HDDs and SSDs to be combined in one volume, with “optimal” utilization of capacity and performance.
In contrast to an SSD cache, the capacity of the SSDs is added to that of the HDDs. But how does QTier work in practice? Let’s find out in this article!
QTier = combination of HDDs and SSDs
QTier describes the combination of HDDs and SSDs. The QNAP NAS automatically creates several storage pools. One each on HDDs and one on the SSDs. These are connected in the background so that they look like a volume/pool to the user.
The NAS tries to sort data depending on usage. Data that is accessed less often ends up on the HDDs, while data that is used often ends up on the SSDs.
This is intended to combine the advantages of the high capacity of HDDs with the speed of SSDs.
Advantage over SSD cache?
But what is the advantage over an SSD cache, which is supported by practically every NAS manufacturer?
We have a similar principle here, but with SSD cache the capacity of the SSDs in the pool is lost. This is not the case with QTier!
If you combine a 16 TB HDD with a 4 TB SSD, you have 20 TB capacity with QTier, but only 16 TB with a regular SSD cache.
Multiple “RAIDs” at QTier
However, in practice it is not that easy. QTier doesn’t simply connect HDDs and SSDs into a RAID 5 or similar.
Instead, a separate RAID is created on the HDDs, SATA and NVME SSDs. Yes, QTier also differentiates between SATA SSDs and NVME SSDs when it comes to division.
This means, for example, if you connect 4x HDDs with 10 TB each with 2x NVME SSDs with 2 TB each in QTier, a RAID 5 would be created on the HDDs (= 30 TB usable capacity) and a RAID 1 (= 30 TB usable capacity) on the SSDs for clean data protection. = 2 TB usable capacity).
So we would effectively have 32 GB of usable capacity here, but one HDD and one SSD could fail without causing any data loss.
If you had 4x SSDs, you could of course also use RAID 5 on them for better capacity utilization, etc.
Likewise, you could also say that you “trust” the SSDs and connect them in a RAID 0, which would increase the capacity to 34 TB, but would result in data loss in the event of an SSD failure.
QNAP doesn’t tell you anything here. You can “freely” adjust the RAID configuration to your liking.
Cold, warm, hot
QTier distinguishes your drives into three groups.
High Capacity = langsamere HDDs
High Performance = SATA SSDs oder SAS HDDs
Ultra Performance = NVME SSDs
Accordingly, when it comes to data, a distinction is made between “cold” data that is rarely used, “warm” data that is used every now and then and “hot” data that is used often.
Frequently used data ends up in the fastest storage class.
However, this does not happen “on the fly”, but rather at certain intervals or according to a schedule, the NAS sorts the data according to access.
Performance in practice
I tried QTier in practice or now use it permanently because I was quite satisfied with the results of the test.
I used the following test setup:
QNAP TS-873A
3x 14 TB HDDs von Toshiba
2x 1TB NVME SSDs von Seagate
10 Gbit LAN
I first connected the 3x 14 TB HDDs in a RAID 5 to get a few “basic values”.
I then set up a “QTier” with the 3x 14 TB HDDs in RAID 5 and the two 1TB NVME SSDs in RAID 1.
Importantly, QTier can be turned on/off on a per-folder basis.
I transferred and downloaded a single 50 GB file to the NAS over 10 Gbit LAN, as well as a 50 GB folder with around 500 individual files.
Here we see that QTier works as it should. Both reading and writing data rates increase by more than 2x. We even get the full 10 Gbit speed when reading.
In the UI we can see that data has been transferred to RAID group 1 (the SSDs).
Apparently new data always ends up on the fastest group in QTier first and is then subsequently distributed among the slower drives. This happens automatically or on a schedule.
Conclusion
QNAP QTier is a really useful feature for combining HDDs and SSDs without “giving away” the entire storage space of the SSDs as is the case with a cache.
It therefore makes sense to combine larger and multiple SSDs with the HDDs. Of course, a pure SSD pool would be even better, but this is very expensive if you have large amounts of data.
QTier worked absolutely perfectly for me in practice. The automatic sorting of data on SSD and HDDs also seems to make sense.
In short, QTier is a big advantage with a QNAP NAS.