Drive Detection & Use:
- The Nx Witness Server application, once installed upon a computing device, detects and analyzes available storage during the setup process.
- Nx Witness will utilize all drives in a Server and writes concurrently to all enabled drives, so the more drives you have in a Server the less throughput you'll see on any individual drive.
- Nx Witness will not allow recording to drives that are less than 10% of the size of all other drives in the system (e.g. an SD Card or USB Flash drive). For example if a user has 10 TB NAS registered at some server all other drives with total space less than 1 TB will be disabled for recording at this particular server. This is done to ensure a correct write-ratio calculation and to improve overall system stability.
- External storage drives can also be assigned via the Nx Witness client. Storage options include local storage to the HDDs available on the server computer, Direct-Attached Storage (DAS), and Network-Attached Storage (NAS).
General Nx Witness Write-to-Archive Process:
- IP Video camera streams are detected and captured by the Nx Witness Media Server and stored in RAM.
- The Nx Witness Server writes captured IP video in RAM to available storage (internal hard drives, DAS, or NAS) once per minute..
- All suitable drives are written concurrently and according to a ratio the system calculates for their size. So, for example, if a single server has multiple sized hard drives Nx Witness will fill up each hard drive at the same rate to ensure that no single drive's system bus gets overloaded.
- Nx Witness keeps some free space at every drive so that performance is not affected. You can find details about Nx reserved space here: https://support.networkoptix.com/hc/en-us/articles/229345767
- When a drive is full Nx Witness will then begin to overwrite non-locked video starting with the earliest (oldest) video on the server across all drives. Thus solid timeline is guaranteed.
- Since 2.6 version Nx Witness keeps system drive blocked for recording if there's any other drive at server which fits minimal requirements and at least 5 times larger than system disk.
- User can not manually modify the archive(delete/add/etc.) using Nx Software
How is hard disk failure managed?
If a single drive in a multiple drive system fails the Nx Witness system will do the following:
- continue writing to all available drives
- create a notification in the notifications panel that a hard drive failure has occurred
- rebuild the archive index after the Media Server is restarted
- If Failover-on-Hard-Drive-Failure is enabled the cameras writing to this drive will be moved to a designated Failover server (starting in v4.0).
Comments
2 comments
How many days is data recorded and stored on server by default?
Hi
Is it still the case the below (NX writing RAM to disk - once per minute) happens in ver 2.5 and 2.6?
•The Nx Witness Server writes captured IP video in RAM to available storage (internal hard drives, DAS, or NAS) once per minute..
How much RAM is reserved for each camera? I calculate 40.8MB may be needed for 3MPIX camera @ 25fps and high quality (5.5Mb/s);
5.55Mb/s / 8-bits = 0.687MB/s * 60-secs = 41.25MB?
What happens for cameras at higher rates? I've often seen cameras running VBR (variable bit rate) running much higher rates with high scene changes and\or low-light\noise.
I've also seen occasional INFO events = "Slow HDD, NX slowing recording". Is this NX trying to slow the camera (if optimized) to fit within buffer limits?
Also, is there a relationship between .mkv file sizes and the buffer - looking at my 1080 25fps files seem to vary between being written every 1 to 4-minutes, but always about 32-35MB in size. Could this be the appx buffer size?
This is a good document regarding disk storage :-) Would you have similar for buffering within NX?
Best regards,
Neil
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