Filesystem performance overheads?

Question

Hi all,Is anyone aware of studies that have been done to measure theperformance overheads that result from using a filesystem? We want toknow the performance loss that we would suffer using a filesystem likeFAT16 on a ramdisk versus using the memory as it is (raw reads andwrites to memory, without considering it as a ramdisk with a filesystem).As far as I understand the performance loss would be miniscule,especially compared to what the filesystem buys us in convenience. But,still I am looking for some hard facts to back up this claim.Thanks & regards,Sachin

Jonathan Bartlett · Accepted Answer

It may be "small" but not "miniscule". For every access you would have to do a context switch and the kernel would have to run just to read data, as opposed to just being able to read it with one instruction and no context switch.

Jon

Gene S. Berkowitz · Answer

FAT16 (and variants) require walking the FAT chain whenever it is necessary to append, truncate, or seek in a file. Depending on cluster size and file size, that can be quite significant, and result in quite noticeable delays. Additionally, depending on the implementation, it's necessary to only allow one process access to the FAT at a time, in order to prevent corruption.

--Gene

Information · Answer

For another take on this topic, you might have a look at this article that compares a database in a ramdisk versus an in-memory database, both on Linux systems.

In-Memory Database Systems

Linux Journal, September 1, 2002

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Or the proprietary version:

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Filesystem performance overheads?

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