![]() ![]() Formatting removes fragmentation issues, especially if the disk is not filled during a recording mission. If the disk is formatted before recording is started, then the likelihood of problems occurring is reduced significantly. Galleon recording software all uses a main memory buffer. Using memory in the computer to buffer data going to disk helps to reduce the impact of the variability of bandwidth to the disk. The techniques described below will reduce the likelihood of problems, but they cannot completely remove the issue. It is possible to mitigate the variability of the HDD write bandwidth. Therefore, it really isn’t possible to give a 100% guaranteed bandwidth which can be sustained into the disk. Managing these bad blocks (and needing to avoid using those locations on the disk), will also impact the capability for the HDD to sustain any particular bandwidth over the full duration of its life. This would only happen if certain factors combine at the same time, causing the disk to spend almost all its time seeking and hardly any time writing to the disk.Īlso, HDDs keep track of bad blocks, which gradually develop (and are detected) over the lifetime of the disks. It is possible (although unlikely) that the disk bandwidth could reduce to much less than normal. Whereas with SSDs, recording bandwidths to HDDs cannot be guaranteed. This also results in more seek time, and less time spent writing to the disk. 1.1.1 Fragmentation of the file systemįragmentation of the files spread across the disk forces the write process to pick new locations for writing to more frequently. These intermittent read accesses will also severely affect the disk access speed. To further complicate the access pattern, the file system will occasionally read from the drives to update file allocation tables or journals. The problem is exacerbated if multiple different channels are being recorded simultaneously (each with two or more files). Writing to multiple files leads to more seek time and less time spent writing to the disk. In the simplest case, this could be a raw data file, and an index file. When recording data, the recording software needs to write to more than 1 file. ![]() if just one of the disks has a seek time delay, all of the RAID array will be affected. Also, the RAID controller will be delayed until all of the disks (4 or 8, depending on the configuration of the recorder) have completed the write cycle. This seek time hugely reduces the effective write bandwidth of the disk. However, sustained bandwidth (for a recording application) are affected to the need for the write head to seek a new location when required. HDD bandwidths can be very high while streaming data to one location on the disk. This is in stark contrast to Solid State Device-based disks (SSDs) which have a predictable worst-case bandwidth. Hard Disk Drives (HDDs) display extreme variations in write bandwidth to the disk. When storage requirements are large, then SSDs are extremely expensive, so HDDs are certainly worthy of serious consideration. However, in commercial environment applications, HDDs could be used, although still not ideal (as explained later in this document). HDDs are not reliable enough to be sensible competition to the SSDs in these circumstances. Galleon Embedded Computing AS assumes no liability arising from any use of information provided within this document.įor rugged environments, SSDs are used for all recording applications. CopyrightĬopyright © 2018 Galleon Embedded Computing AS. Binary prefixes Ki (kibi), Mi (mebi), Gi (gibi), and Ti (tebi) denote 2^10, 2^20, 2^30, and 2^40 respectively.ĭates printed in numerical format are in the order day month year.Decimal prefixes k (kilo), M (mega), G (giga), and T (tera) denote 10^3, 10^6, 10^9, and 10^12 respectively.IEC prefixes are used to separate between decimal and binary multiples. ![]() Portable Planning & Debriefing System (PDS). ![]()
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