[HN Gopher] Maintaining sufficient free space with ZFS
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       Maintaining sufficient free space with ZFS
        
       Author : DerekBickerton
       Score  : 35 points
       Date   : 2022-10-23 20:59 UTC (2 hours ago)
        
 (HTM) web link (taras.glek.net)
 (TXT) w3m dump (taras.glek.net)
        
       | londons_explore wrote:
       | I have certainly written code which consists of "while (free disk
       | space is less than X) {, delete oldest log file}".
       | 
       | Such code would break on zfs.
       | 
       | Is there even a better way to achieve "I want all spare space to
       | be filled with logfiles, but I never want to run out of space."?
        
         | nisa wrote:
         | `reservation` and `refreservation` might work. Set a high
         | default for the pool and a low override for the logfiles
         | dataset.
         | 
         | Using this for several databases on a small SSD to avoid that
         | snapshots fill the disk and the least important database will
         | be out of space first.
        
         | londons_explore wrote:
         | One could imagine an "opportunistic storage" flag on a file
         | which means 'consider this file deletable if you ever need the
         | space'.
         | 
         | It would be especially good for caches of remote files or data
         | that could be recalculated on demand.
         | 
         | We already have lots of similar things for RAM - for example
         | Javas SoftReference.
        
       | [deleted]
        
       | lousken wrote:
       | is 90% used space even good with ZFS these days? I always reserve
       | 25% in order to keep fragmentation in check
        
       | mustache_kimono wrote:
       | I mean 5-10 seconds for the free space to be updated doesn't
       | sound extraordinary? With all the accounting ZFS has do, doesn't
       | this sound like something you would want running asynchronously
       | in the background? The blog makes a point (with references) of
       | ZFS being transactional, but, as a related matter, it's also COW,
       | one would assume finding/guaranteeing "free" space is much harder
       | than it would be on a traditional filesystem.
        
         | toast0 wrote:
         | It's clearly not extraordinary, it's normal for ZFS. UFS2 on
         | FreeBSD does is too, it also has snapshots, but isn't generally
         | COW.
         | 
         | The first time you delete something bit and it doesn't show up
         | in df right away, it might be surprising though. Or this case
         | where automation deleted more than expected because the author
         | wasn't aware of the need to wait.
        
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       (page generated 2022-10-23 23:00 UTC)