Dvr hard disk file system

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They can also be accessed locally by computers on the same network. Users have too many doubts regarding how to access DVR hard drive. Nowadays security cameras majorly capture analog images. The DVR converts these analog images into digital and stores them on the hard drive after compression. It can handle the inputs of several cameras. Users will be able to view all these images and videos at a time or one by one, according to their preference.

The most important things to a security camera system are the hard drive, the device in which security footage is stored. It allows a user to access the recorded video from their security cameras. In that case they need to recover that data. DVR data recovery is challenging and requires technical expertise to restore deleted videos and images. Journaling also ensures that steps that must be performed together atomically actually are.

Consider for example appending data to a file. The third affects the integrity of the data in the file. If the system crashed after the additional blocks were taken from the free-space area on the disk but before they were actually associated with the file, those blocks would become lost until some filesystem repair process noticed them. Filesystems may journal just the metadata or both the data and metadata.

Journaling both the data and metadata is the most conservative route, but can come at a high performance penalty since the data must be written twice — once to the journal and then to the disk.

However there is very little chance that files will have corrupt data in the event of an ungraceful shutdown since both the data and metadata will be consistent. Journaling only the metadata guarantees that the structure of the filesystem is valid after an ungraceful shutdown. However the data in the files may not be valid, depending on when the data is committed to the drive. To see how this can happen, consider an application writing data to a file.

As more data is written, the filesystem extends the file, allocating more space as needed. Even if the system were to shut down ungracefully, the file size and block allocated to the file are preserved in the journal and can be recovered by replaying the journal on restart.

However, the data is not journaled and may be written to disk after the metadata is journaled. So what happens on an unclean shutdown? If the filesystem ensures that all data is flushed to the disk before the journal is updated, then this is almost as good as journaling both the data and metadata.

The filesystem structure will be fine after a crash, but the files may be corrupted — rather than the data that was supposed to be written, the file will contain whatever happened to be on the disk at the time. Whoever has access to the file now has access to that information. Our simulated DVR simultaneously records eight shows and plays back two. Each of the ten threads performs reads or writes in a tight loop, effectively hammering the filesystem.

For the purposes of characterizing performance, we will assume that each record is capable of buffering up to five seconds of writes and that playbacks read 2 MB at a time. What this means is that on the record side we care about the average access time when computed over a moving window that spans five seconds.

The peak average will indicate the limits of what we are guaranteed. Similarly for playback, the average over two 1 MB reads is relevant, and twice the peak average is what the DVR playback will need to contend with. To obtain a close to worst-case seek pattern, the drive was divided into ten equal parts either using partitions or large contiguous files.

The first and last parts were allocated for playback reads and the middle eight for record writes. The first and last parts correspond to the outermost and innermost parts of the drive, so satisfying the two streams of reads means full-stroke seeks. This randomization within each disk area combined with all threads running simultaneously means that at any given time there are read and write requests spanning the entire platter.

To measure the access times, all ten threads were started. Only after all threads had collected samples were the threads shut down. While not as power efficient as the 2.