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I've initialised one large primary partition with the -T small flag to mke2fs, small on the system is configured as follows:

    small = {
            blocksize = 1024
            inode_size = 128
            inode_ratio = 4096
    }

This is a 800 GB SSD (cloud drive) which will be a home for the 10+ million small files, ranging from ~10KB to ~100KB.

I tried to go thoroughly the man pages of mount and figure out the best combo of flags and here's my list:

  • rw - read and write
  • nosuid - no need for user or group ID on execution
  • nodev - block dev files should never appear in here
  • noexec - files with exec bit set are also not welcome
  • auto - allow mount -a
  • nouser - only root can (re)mount
  • async - async writing
  • relatime - update access time only when files are modified.
  • data=ordered - presumably should improve read performance
  • errors=remount-ro - stop writing when errors
  • discard - recommended for SSD
  • auto_da_alloc - fight filesystem corruption in case of power failure (perhaps not needed, as this is a cloud drive?)
  • inode_readahead_blks=16 - file system will be a home for the great bunch of small files, hence big readahead should be nothing more but a performance penalty. I didn't know the optimal value for files of average size 50KB, so just put here twice as less value as the default.
  • debug

I really need a second opinion from someone more experienced in these matters. I'm particularly unsure about the discard, relatime, data=ordered, auto_da_alloc, inode_readahead_blks and other flags, which I have missed or misunderstood. How dangerous is data=writeback? How much data I may loose with such flag, is it just the last 5 sec (default value of commit)? Other insight regarding this exercise?

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    Why have you chosen ext4 for your filesystem? – Michael Hampton May 14 '16 at 22:03
  • My playground here is the production server, hence I need fs that was well tested by many and proven being stable and efficient. – NarūnasK May 14 '16 at 22:13
  • What kind of storage controller are you on? Is it battery backed? This will have a pretty significant impact on some flags you can/cannot safely use that may have some pretty big performance impacts. – dodexahedron Jun 13 '16 at 1:47
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You should probably just use the XFS filesystem for this.

ext4 is not well-suited to this workload because you're on an SSD and have a stupid-high file count. There's a reason Red Hat now defaults to XFS.

  • Thanks, but based on this, XFS perhaps is the last thing I should use for the great number of small files, unless you can argue these results. – NarūnasK May 15 '16 at 8:08
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    Do what you want... or just test with your own data set. – ewwhite May 15 '16 at 8:09
  • Your statement that I should just use XFS is not very convincing, especially when there's evidence showing otherwise... – NarūnasK May 15 '16 at 8:16
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    Okay, then you've arrived at your own conclusion. – ewwhite May 15 '16 at 8:18
  • @NarūnasK Your statement that I should just use XFS is not very convincing And that benchmark you linked to isn't very convincing, either. Benchmarks that don't specify the hardware being used are useless. – Andrew Henle May 16 '16 at 9:59
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Why not consider using ZFS on linux? ZFS is definetly superior to ext4 and it's considered production ready on linux. See http://www.phoronix.com/scan.php?page=news_item&px=MTc4NTM

It's not difficult to install; see http://zfsonlinux.org/ for installation info.

  • Thank you for your input. zfs was noted and expelled from the list due to the fact, that it is not supported in Debian (because of the licensing) and its greedy constraints of the memory. I agree, that zfs is superior system and RAM these days is relatively cheap, however decisions already made. – NarūnasK May 14 '16 at 23:14
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    @NarūnasK zfs was noted and expelled from the list due to the fact, that it is not supported in Debian (because of the licensing) So you've already decided on your solution and you're now force-fitting your problems into that solution. That's backwards. – Andrew Henle May 16 '16 at 10:04
  • No, these answers just don't answer his question. He didn't ask for another file system. He asked about the flags for mounting the file system he's already chosen. – dodexahedron Jun 13 '16 at 1:44

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