Applies to: WAVE
Summary:
Once installed on a computer, the WAVE Server application detects and analyzes available storage during setup. The Server application 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.
Background Archive Distribution and Retention:
Video from a camera is always written to the server to which it is connected. Cameras can be moved between servers, but the recorded video stays where it was and never moves with the camera. A new video is written on the new server. A recorded video is called an archive.
If a server has multiple drives, the video archive is divided between them to improve reliability and balance the load on each drive. Nevertheless, video playback is seamless even when different parts of the archive are stored on other drives or servers.
Other data is stored in a space occupied by data, not from the VMS; this space is never recorded. In addition, a certain amount of the total capacity is reserved space that will not be used for recording. Numbers vary depending on the software version and server configuration; typically, 10-30 GB is reserved for local storage, and 50-100 GB is reserved for external storage.
Available Space:
The remaining disk storage is considered available space, whether recorded on or is currently free space. The archive is recorded according to available space.
If there is no free space on a given storage device, the system will automatically delete outdated recordings to free space for a new archive. By default, the oldest archive is deleted first. However, there are two unique properties a given camera can be granted that affect archive retention. One prevents the archive from being deleted before a certain number of days has elapsed. The other requires that the archive be deleted after a certain number of days has elapsed. These are the only cases in which the system will actively determine storage deletion.
An Illustration of the storage life cycle:
Storing Archive on Multiple Drives:
Servers can have any number of storage devices. Recording to some can be disabled manually or automatically when they are too small or are the primary OS partition. USB drives are disabled by default but can be enabled manually (though for ARM devices, they can be enabled by default).
Enabled drives can be one of two types—main or backup. Primary storage is used to record archives, and backup is used to store extra copies of some recordings. At any given moment, a drive can be assigned only one type, but because it is possible to change a drive's type, it is possible to have different types of recording (primary and backup) on one drive.
If there are multiple storage locations of the same type (primary or backup) on a server, the recorded archive will be split between them in proportion to their available space, as shown below:
When a server has multiple storage locations of the same type, recorded archives are distributed separately by type in proportion to the available space for each type.
Write bitrate (the amount of data processed per unit of time) will correlate with the amount of available space—in the illustration above, disk one will have a higher bitrate than the others.
The distribution of recorded data depends on the amount of available space, not free space. If you have two similar drives, but some other data occupy part of drive #2, the recording speed will be higher for drive #1 because the available space for this drive is higher. Also, because the archive recorded by the System does not reduce the available space, recording speed doesn’t depend on how much available space is currently used.
For example, if two similar drives are already full, you add a third drive with the same space as the first two, but it is empty. The recorded data distribution depends on the available space, so new recordings will be distributed evenly between all three drives. Even though there is plenty of free space on the third drive, outdated footage on the first two drives will be deleted to free up space for new recordings – the archive must be split evenly between all three drives because they have the same available space.
This is done to balance drive usage and avoid all cameras being written to one drive, which might need more speed to record such data.
Servers Sharing the Same Drive
Setting up recording from multiple servers to the same drive is possible. However, it is very important to split the drive into different partitions and attach separate partitions to each server so that another cannot delete the archive written by one server.
If you add one partition to multiple servers, they will treat free space on that drive as available and use it for recording. Data recorded by one server will be considered “other data” by the other server and will reduce the amount of available space but will not be overwritten. However, if multiple servers use the same folder and the archive for anyone is reindexed (see "Reindexing Archive"), archive footage from the other servers can be deleted.
If different servers have different recording speeds, storage will be divided unequally. After the archive fills storage, each server will manage only the space its data occupies, as shown in the diagram below.
WAVE Write to Archive Process:
-
Video camera streams are detected and captured by the WAVE Media Server and stored in RAM.
-
The WAVE Server writes captured 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.
-
If a single server has multiple-sized hard drives, WAVE will fill up each hard drive at the same rate to ensure that no single drive's system bus gets overloaded.
-
WAVE keeps ten percent free space by default on every drive so that performance is not affected. Our article, How to configure Reserved Space, provides more details.
-
When any storage drive (e.g., X) is filled, WAVE will begin deleting the recorded video, starting with the earliest/oldest video on the server across all drives, until there's enough space to record a given amount of data. As a result, a solid timeline is guaranteed.
-
WAVE prevents recording onto the system drive if any other storage drive is installed on the server that meets the minimum requirements and is at least five times larger than the system disk.
- Users cannot manually modify the archive (delete/add/etc.) using HVA Software.
Hard Disk Failure Management:
If a single drive in a multiple-drive system fails, WAVE will do the following:
-
Continue writing to all available drives.
-
Create a notification showing a hard drive failure.
-
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.