These are some personal notes which might help other advanced home users.
Selecting a NAS:
10 Gb/s network connection is a must. A SATA HDD (7200 RPM) can reach around 200 MB/s sequential I/O performance and a SATA SSD around 500 MB/s. Only this requires more than 1 Gb/s network bandwidth. When you have a RAID group, I/O throughput increases, so 10 Gb/s is a must. It can be on-board or available with a PCIe adapter. However, PCIe support requires x86 based NAS which is more expensive.
ARM-based NAS is probably enough for normal home use. I have not seen anything yet where CPU is the bottleneck.
If you only need a safe external storage (safer than a single external disk), you might live with RAID-1 and have a 2-bay NAS. If you need something better, you will want to use RAID-5 or 6, so you need at least 3 or 4 disks. Then you might want to have a few SSDs (either for cache or just for a faster but smaller volume for virtual machines). So I think 8 (3.5") or 5 (3.5") + 4 (2.5")=9 bay NAS is a sweet spot. Probably you are going to spend more on disks, so it is a good idea to stretch the budget for the NAS.
If you will install large disks (>8 TB) (and probably you will install eventually), it is safer to use RAID-6 (check RAID Reliability Calculator]). In this case 4 disks are too less, you will lose 2 to parity, so you will lose 50% of the storage capacity like in RAID 10. So again I think 5 (HDD) + 4 (SSD)=9 bay units are a good choice.
Usually the installed memory is minimal, and it is a bit difficult to upgrade the RAMs later (you need to remove the disks etc.). Because the lifetime of a NAS is quite long (probably 5+ years), it makes sense to upgrade RAMs to maximum supported.
Because of all above, I decided to move (from an old 4-bay unit) to TS-932PX. It is probably the cheapest option that satisfies everthing I said above. I have upgraded the RAM to 16 GB and using it with 10 Gb/s connection, again with a QNAP switch (QSW-M408-4C).
There are two limitations of this model (and I think all ARM based models): 1) ZFS is not supported (it has QTS system), 2) there are no PCIe expansions. At the moment, I need to spend around 1.5x more to get something x86 based. One important point is if you get a ZFS supporting NAS later, you cannot directly move your disks to that, you need to do a backup and restore.
Take home message:
If you need only a safer external storage, get a 2 bay NAS, configure a RAID-1 pool and use.
If you have budget constraints (or want to spend more on disks), get a 8/9 bay NAS and use RAID-6 with at least 5 disks.
If you have no budget constraints, get a 9+ bay x86 based NAS (e.g. TS-h973AX or TVS-h1288X, which are probably 1.5-2x and 4x more expensive than TS-932PX).
Hints on first setup/initialization:
If you have an 8/9 bay NAS, it is a good idea to have two SSDs in RAID-1 group/storage pool, and use this as a SYSTEM volume (the first volume you create becomes SYSTEM volume). Main reason is when you use your actual disks as SYSTEM volume, it limits your options, i.e. you cannot “safely detach” the pool because it contains the SYSTEM volume. It is I think the best to keep this separate from the actual data, so you can freely move the pool to another NAS when needed. This leaves 2 SSD bays free, which can be used for cache or pure SSD volume.
I am not sure what should be the size of SYSTEM volume. I made it 100 GB, it uses less than 20 GB just after it is setup.
If you need random I/O performance (virtual machines etc.) and the storage capacity needed is low, there is no point using HDDs. You can just get two SSDs and make a RAID-1 group.
If the NAS is in other room or you do not care too much about the noise of the disks, check also the enterprise HDDs. Sometimes they are even cheaper than consumer/SMB ones (e.g. WD Red Plus vs. Red Pro vs. Ultrastar HC550). I found 18 TB Ultrastars even cheaper than Reds, so I am using them.
Do not forget:
- When you have a NAS, you need a UPS.
Recommended first install of 8/9 bay NAS:
Start NAS without any disks attached.
Install 2 SSDs, make a RAID-1 pool and create a volume named SYSTEM, it will be used by QTS.
Install other disks, and configure as you like.
- A change (synchronization, rebuild, migrate) in a large RAID-5/6 array takes a lot of time (a few days with 18TB disks).
Performance (internal file system test) of TS-932PX and the disks (5x WD Ultrastar HC550 18TB HDD RAID-6 and 4x WD Red SA500 500GB SDD in two different RAID-1 volumes) are below. SYSTEM and FAST are on different SSD RAID-1 volumes, MAIN is on HDD RAID-6 volume.
Start testing! Performance test is finished 100.000%... VolID VolName Pool Mapping_Name Throughput Mount_Path FS_Throughput 1 SYSTEM 2 /dev/mapper/cachedev1 1012.00 MB/s /share/CACHEDEV1_DATA 882.76 MB/s 2 MAIN 1 /dev/mapper/cachedev2 551.70 MB/s /share/CACHEDEV2_DATA 775.76 MB/s 3 FAST 3 /dev/mapper/cachedev3 1006.00 MB/s /share/CACHEDEV3_DATA 901.41 MB/s
Performance of same TS-932PX configuration when copying a large file from/to NAS is around 600MB/s.
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