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Tutorial Setup consideration: NAS Disks vs LAN Environment

When you finish preparation stage - what disk(s) or disk group(s) is best for your data operation mode, don't forget for a specific limitations - your network (possible bottleneck).
In this case I will take into consideration frequent mistakes in such preparation stage, that have impact to your satisfaction. Specially for LAN.

First - wired network is wired (faster, secure, manageable), then hen you have a chance to prepare some wired network across your home/office don't hesitate to do it. When there is reasonable "NO", ok - it's also kind of solution.

I will provide some reason, why it is reasonable. Then we need start from disk performance.

1. Operation Disk speed in your NAS, check
(when NAS is already purchased/used and old disk(s) is/are ready for a replacement):
For Read speed
open SSH and use command hdparm with two different options:
-T ... for speed of disk reading include Linux OS cache ... important for your internal system setup
-t ... for clean speed of disk reading exclude Linux OS cache (buffered) ... important for your LAN speed analyze and setup
... detailed command description is here

Lets do it:
hdparm -Tt /dev/sda or /dev/sdb, /dev/sdc, ....up to your disk/group config

you can get answer like this:
/dev/sda: Timing cached reads: 1898 MB in 2.00 seconds = 948.90 MB/sec Timing buffered disk reads: 466 MB in 3.04 seconds = 153.18 MB/sec

For Write speed
Method no. 1
dd if=/dev/zero of=/tmp/output conv=fdatasync bs=384k count=1k; rm -f /tmp/output

you can get answer like this:
1024+0 records in 1024+0 records out 402653184 bytes (403 MB) copied, 0.668618 s, 602 MB/s

Method no. 2 - more accurate - clear measure of disk speed and not busted by memory (cached), based on sync the filesystem to get rid of the caching effect:
sync ; time sh -c "dd if=/dev/zero of=testfile bs=100k count=1k && sync" ; rm testfile

you can get answer like this:
1024+0 records in 1024+0 records out 104857600 bytes (105 MB) copied, 1.28967 s, 81.3 MB/s real 0m2.557s user 0m0.007s sys 0m0.571s

you can use different Block size parameter "bs=" what is more suitable to your test scenarios, e.g. "bs=4k" for 4K Blok size

your disk (disk group) speed for LAN operation is based on above evaluation:
- 153.18 MB/s for READ = 1225.44Mb/s
- 81.3 MB/s for WRITE = 650.4Mb/s

So then you need for max. Disk (group) utilization:
2Gbps LAN for READ operation
1Gbps LAN for WRITE operation
otherwise, when you will use 1Gbps LAN, your READ operation from NAS (Disk) will drop to max. 1024Mbps, what is just 83,6% possible utilization of your disk performance.

What is does mean for your data speed loses = minus 25Mb/s =3.1MB/s ..... and it doesn't need your action for an improvement.

What will happen when you will use faster disk?

Chapter 2 - best fit LAN environment to your disk speed or up side down again
Now you Know how to check your operation speed of your disk(s)/group.

There is still valid basics:
- you have E2E 1GB LAN architecture between your NAS and devices. For better understanding - wired LAN.
- YES and YES again two different 1G switches from different vendor (even from same vendor) will provide different performance outcomes (another story).

Few practical calculations for your LAN setup:

As you can see in table (above):
1. You can utilize your 1G LAN speed with really (practically) slow disk, that was purchased with high hopes (performance point of view). Limit of the 98% utilization is 125MB/s write speed in NAS.
2. Same for 2x1G LAG, Limit of the 98% utilization is 250MB/s write speed in NAS. What is good speed for basic disk usage, but still slow.
3. What is important, there is a limitation of Synology maxed 4x1G LAG ... 512MB/s write speed in NAS.

- if you need use SSD disk for better performance, you need use LAG. And 4x1G LAG is minimum - as you can see in table above
- otherwise your disk performance is a wasted investment.

for >39% 10G single NIC utilization you need SSD basic disk with 500MB/s (measured)
for >98% 10G single NIC utilization you need RAID0 with min 4x SSD with 500MB/s (measured). No way for other RAID(SHR) scenarios. Then you need adjust your NAS operation model (disk groups, number of bays) to this kind of utilization. Don't start from number of NAS bay as main choice rule!

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