Disk Recording Overwrite Problem
<p>[TOC]</p>
<h3>I. Overview of video overlays</h3>
<h4>1、Single-disk video loop overlay</h4>
<p>The video partition of the disk is organized and managed according to the same size video unit, i.e., the partition is divided into video blocks of the same size (according to the size of the disk or according to the size set by the user to determine the size of the video unit when formatting), and the video data is written sequentially, and then written from the beginning after writing once to achieve cyclic coverage by absolute time (not dependent on the system clock, even if the system clock (even if the system clock is confused, the video data is also written in the order of overwriting).</p>
<h4>2、Multi-disk video switching and overwriting</h4>
<p>Multiple-disk video switching is a cyclic overwrite with reference to the system clock (no other reference information). The following conditions need to be met for the video disk switching action to occur.</p>
<ul>
<li>The existence of multiple disks and the menu selects multiple disks all for one type of use.</li>
<li>The currently recording video unit of the video disk being recorded is written out and is ready to be switched to the next video unit.</li>
<li>The oldest recording time of the current recording disk, when it is newer than the latest recording time in one of the disks to be recorded.</li>
</ul>
<h3>II. Common Problems</h3>
<ul>
<li>
<h4>Multi-disk not covered by the rules</h4>
<p>Multi-disk not covered the oldest video, but the intermediate video is covered.</p>
</li>
</ul>
<h3>III. Analysis steps</h3>
<ul>
<li>
<h4>Multiple disks not overwritten according to rules</h4>
<p>The following steps can be followed to troubleshoot the causes of the problem one by one.
1, Whether the system clock back phenomenon occurs.
2, Whether there is a disk not found in time during the boot process.
3, Whether there are bad blocks on the disk.</p>
</li>
</ul>
<h3>IV. Operating instructions</h3>
<ul>
<li>
<h4>Multiple disks not overwritten according to rules</h4>
</li>
</ul>
<h5>1、System clock regression phenomenon troubleshooting</h5>
<p>If the system clock backward occurs, the end time of the current video disk, is the end time of the backward time, in this case, will lead to the calculation of the starting and ending time of the disk is wrong, thus causing the selection of the disk switching action, there will be a miscalculation. The phenomenon of time rollback is as follows.</p>
<p><img src="http://118.195.179.210:9000/server/index.php?s=/api/attachment/visitFile&amp;sign=8de0d8ae3076eebc93290be9edde5a0e" alt="" /></p>
<h5>2、The boot process exists disk not found in time phenomenon troubleshooting</h5>
<p>The boot process, a disk identification slower, if the last shutdown before the video is recorded in the disk of the slower identification, the existence of the boot first recorded to another disk, thus causing the video disk switching error. Eventually lead to two disks in the video, can not follow the chronological order, first cover the oldest video.</p>
<h5>3、Whether there are bad blocks disk troubleshooting</h5>
<p>During the recording process, if a disk error is reported, the disk will stop the video, and switch to another disk for video. After the recovery of the failed disk, if it is still switched to the failed disk according to the time, then briefly recorded to another disk in the video data, can not follow the principle of first-in-first-out coverage; if the time has been switched to another disk for recording, the two disks in the video, there will be a time period crossover phenomenon, part of the video will be in the principle of multiple disk switching, was covered off early.
Disk failure problem, you can check the user logs to confirm whether there is a disk alarm in the storage class logs, or through the platform to check the storage failure alarm. Hard disks can also be checked for bad block problems by using the PC scan tool.</p>
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