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Does writing to ext. drives use the boot drive as temporary cache?

P

PkennethV

macrumors 6502a
Original poster
Aug 16, 2006
853
9
Toronto
Does anyone know whether the boot drive is written to at all (as a cache) when, for example, you are downloading a file via Safari and the chosen destination for the file is an external drive?

How about if you are transferring a file from one external drive to another external drive? Does the data just go from the source drive, through RAM, then to the destination drive, or does the file (or parts of the file) get stored on the boot drive before making its way to the destination drive?

thanks!
 
satcomer said:
All Internet cache is saved on your Internal hard drive. You just specified the Download of Safari location only.
Click to expand...

To clarify, I'm asking whether *download files* get temporarily stored on the boot drive at any point whatsoever (whether in small kilobyte chunks or in whole) before being "moved" behind the scenes to the specified external drive - or whether the downloaded file goes directly from RAM to the specified external volume.
 
PkennethV said:
To clarify, I'm asking whether *download files* get temporarily stored on the boot drive at any point whatsoever (whether in small kilobyte chunks or in whole) before being "moved" behind the scenes to the specified external drive - or whether the downloaded file goes directly from RAM to the specified external volume.
Click to expand...

No you are trying to overthink the situation. The Finder pointer is a pointer Apple gives to one to tell the download togo to your preferred setting. It just straight to that set location.

What will blow your mind is aliases and sim links and trying to tell the difference. :p
 
Last edited:
satcomer said:
No you are trying to overthink the situation. The Finder pointer is a pointer App,e gives yo one to tell the download togo to your preferred setting. It just straight to that set location.

What will blow your mind is aliases and sim links and trying to tell the difference. :p
Click to expand...

I know full well the difference between symbolic links and aliases...I create symlinks regularly as a hack way to synchronize preferences of apps between computers via Dropbox and also to relocate the cache location of screen capture recording software (some of them temporarily record to the boot drive, even if you have set the scratch disk to an external drive, and only upon saving the screen capture file, does the app relocate the file to the specified scratch disk) as well as the cache location of cloud storage services.

I'm asking my original question because I will be downloading terabytes of uncompressed media and would like to know whether, even if I set the destination of the file to be an external volume, whether it would put any unneeded wear on the SSD boot drive. Because if it does, then (ironically, in reference to your reply), I would create a symlink of the download cache on an external HDD so it skips the SSD entirely.

I do have tools to monitor the read/write activity of specific volumes, but since the boot drive is always being written to at all times for various reasons, I'm having difficulty concluding for sure whether the write activity is because of the files I'm downloading or not.

Even if the file ultimately ends up on the external drive, it doesn't mean that the boot drive was not written to. It can be that the files are stored in 1MB chunks (for example, possibly even smaller) on the boot drive, and is transferred in 1MB segments over to the external volume as a background/system process. If this was the case, even though the cache files would be extremely small, over time, the boot drive would still have accumulated terabytes of writes over the course of terabytes being downloaded (again, unless a symlink was created - and the entire point of my question is to know whether this would be necessary).
 
The only I kind of the the download location you choose is written to your Safari Preferences in /YourHardDrive/Users/YourUserName/Library/Preferences/, only that you changed the saved location.
 
PkennethV said:
Does anyone know whether the boot drive is written to at all (as a cache) when, for example, you are downloading a file via Safari and the chosen destination for the file is an external drive?
Click to expand...

The boot drive is not written to (in any significant way) if you are using the "Download linked file as..." dialog. e.g., downloading the HP Printer drivers (~500MB):

Code: 
$ iostat 10
          disk0           disk2           disk3       cpu     load average
    KB/t tps  MB/s     KB/t tps  MB/s     KB/t tps  MB/s  us sy id   1m   5m   15m
   17.12  10  0.17    63.36   7  0.46     2.13   0  0.00   1  1 98  1.34 1.99 1.64
   14.29  10  0.15     9.00   0  0.00     0.00   0  0.00   1  1 97  1.29 1.96 1.63
    7.72   3  0.02   125.77  13  1.61     0.00   0  0.00   2  4 95  1.24 1.93 1.63
    9.33   2  0.02   127.80  61  7.60     0.00   0  0.00   2  5 93  1.20 1.90 1.62
   18.17  10  0.18   125.18  72  8.76     0.00   0  0.00   2  5 93  1.10 1.85 1.60
   17.00   0  0.01   128.00  70  8.80     0.00   0  0.00   1  5 93  1.08 1.82 1.60
   27.84  29  0.80   128.00  99 12.40     0.00   0  0.00   2  6 92  1.15 1.81 1.59
   13.32   4  0.05   127.07 119 14.72     0.00   0  0.00   2  6 92  1.20 1.80 1.59
    5.00   1  0.00     0.00   0  0.00     0.00   0  0.00   1  1 98  1.17 1.77 1.58

As you can see, only one drive is written to during this operation, and it is the destination drive.

I cannot imagine any circumstance where copying from one external drive to another would make use of the boot drive (unless you did it on purpose).

A.
 
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