How does Nx Witness manage storage?

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% the size of the largest drive 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:

1. IP Video camera streams are detected and captured by the Nx Witness Media Server and stored in RAM.
2. The Nx Witness Server writes captured IP video in RAM to available storage (internal hard drives, DAS, or NAS) once per minute.
3. 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.
4. Nx Witness keeps some free space at every drive so that performance is not affected. You can find more details by reading our article about adjusting reserved disk space.
5. When any storage drive (e.g., X) is full, Nx Witness will begin to delete recorded video starting with the earliest/oldest video on the server across all drives until there's enough space on the drive to record a given amount of data. As a result, a solid timeline is guaranteed.
6. Nx Witness prevents recording onto the system drive if there's any other storage drive installed on the server which meets the minimum requirements and is at least 5 times larger than system disk.
7. 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.

Adding storage afterward

Sometimes people will add storage to an existing system, and we noticed this might cause some confusion due to the design of how storage is managed by the VMS.

As written above, the VMS will fill up each hard drive at the same rate to ensure that no single drive's system bus gets overloaded. For this reason, after storage is added, and the oldest storage drives are full, it does not mean that all new data will be written only to new storage, due to the reason that the VMS server writes data at an equal rate to all storage drives. So, if there is no empty space on the oldest storage drives, it will recycle old data to free up space for new data.

Newly recorded data will be divided equally between all storage drives, so the oldest storage will be filled at a slower pace than before and the archive retention period will slowly increase until all drives haves filled up with an equal percentage of data.

In the meantime, the server provides an estimate for all available storage space and the predicted archive retention time, will be available as soon as all drives hold an equal percentage of data.

Typically, after X months from the date that new storage drives have been added, all storage drives should hold an archive for X months if the predicted archive retention time is also X.

Questions

If you have any questions related to this topic, or you want to share your experience with other community members or our team, please visit and engage in our support community or reach out to your local reseller.