[Discuss] Reducing wear on SSD drives - worth the effort and, if so, how?

[Derek Martin]

On Fri, Nov 18, 2022 at 11:05:52AM -0800, Kent Borg wrote:
> I put /tmp and /var/tmp in RAM disks, figuring that would move some
> background activity off the SSD.

Rich already pointed out a potential downside of this... here are a
couple other points to consider, which you might not have:

 - /tmp and /var/tmp have different intended use cases; /var/tmp is
   meant for temporary files that should survive a reboot.  They won't
   on a ramdisk, so if you have applications using it properly, they
   will be affected.  What that means in practice will obviously
   depend on the application...
 
 - You never really know what applications are using /tmp or /var/tmp,
   and how much storage they are using.  An example from--wow, 21
   years ago--when I was sysadmin at MCL (I'm going to assume my
   memory is accurate despite the time frame, but offer the caveat
   that it may not be):  
   
   The mail server (which was set up before they hired professional
   sysadmins, for whatever that's worth) ran UW IMAP.  The size of
   /tmp was some small-but-seemingly-reasonable size--I don't remember
   exactly but say 200MB or something like that (remember, 20+ years
   ago). After a while people started to experience random failures
   with their IMAP folders, and it took us some time to figure out
   why...  What actually was happening was that when you expunge
   messages from your folder, the imap server was creating a temporary
   copy of your folder in /tmp, and then copying it back to where it
   was supposed to live.  The filesystem was not sized appropriately
   for that use case, and we ended up needing to make it much larger
   to accommodate it.

   Were I to have been the one to set up the server, I would've
   allocated /tmp to be significantly larger than it was, but still
   not likely large enough to accommodate this usage, having been
   unaware of this at the time.

   Point being, if you're running some application like this that
   consumes much more temporary storage space than you anticipate, it
   will exacerbate the issue Rich pointed out, and also increase the
   likelihood you'll experience OOM situations causing your other apps
   (or the same one) to crash randomly if you don't have enough RAM +
   swap to cope.

-- 
Derek D. Martin    http://www.pizzashack.org/   GPG Key ID: 0xDFBEAD02
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