50 Years in Filesystems: 1974 Unix V7

Re:50 Years in Filesystems: 1974 Unix V7 by musicale on Thursday May 11, 2023 @02:06AM (#35898280)

Point taken. In any case, single-writer helps with concurrency and consistency. For V7 Unix, I think one solution could be to split the file into blocks, each with a single writer. Admittedly this makes reads of the whole file more costly, so one has to be careful about the block size.

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Re:50 Years in Filesystems: 1974 Unix V7 by monocasa on Thursday May 11, 2023 @02:50AM (#35898636)

> Admittedly this makes reads of the whole file more costly, so one has to be careful about the block size.

Maybe? You're probably locking each block at a time in the buffer cache during reads anyway.

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Re:50 Years in Filesystems: 1974 Unix V7 by jasomill on Thursday May 11, 2023 @03:41AM (#35899040)

N.B.: in V7 (and 32V), inodes are locked identically for both writes and reads[1],

    if((ip->i_mode&(IFCHR&IFBLK)) == 0)
      plock(ip);
    if(mode == FREAD)
      readi(ip);
    else
      writei(ip);
    if((ip->i_mode&(IFCHR&IFBLK)) == 0)
      prele(ip);

I imagine a more serious bottleneck to random read/write concurrency would have been disk performance.

Average seek time / rotational latency (years by manual copyright, so estimated):

RL02 (1978): 55 ms / 12.5 ms RK07 (1978): 36.5 ms / 12.5 ms RA81 (1982): 28 ms / 8.3 ms RA92 (1989): 16 ms / 8.3 ms.

Note that the RL02 (and V7) and RA92 mentioned in the article are separated by about a decade.

[1] https://github.com/dspinellis/unix-history-repo/blob/Researc...

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