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Top Forums Shell Programming and Scripting Block device fs vs normal directory Post 302465717 by stevenswj on Saturday 23rd of October 2010 08:20:39 PM
Old 10-23-2010
Block device fs vs normal directory

I talked with this guy who seems to think loop mounting a fs ext3 image on a directory, as opposed to just using the underlying filesystem, will work better as far as IO conflicts. I have no idea why this would be better? I haven't been able to contact him.

Basically we have a daemon that creates a bunch of files on a directory, and constantly reads and writes to them. This has resulted in many io conflicts such that some reads and some writes are being blocked.

Why would a block device work better than a normal directory as far as IO conflicts are concerned?

Moderator's Comments:
Mod Comment Double post. Continue here

Last edited by Scott; 10-23-2010 at 09:25 PM..
 

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mount.crypt(8)							     pam_mount							    mount.crypt(8)

Name
       mount.crypt - mount a dm-crypt encrypted volume

Syntax
       mount.crypt [-nrv] [-o options] device directory

Options
       -o options
	      Set further mount options. mount.crypt will take out its own options it recognizes and passes any remaining options on to the under-
	      lying mount program. See below for possible options.

       -n     Do not update /etc/mtab. Note that this makes it impossible to unmount the volume by naming the container - you will  have  to  pass
	      the mountpoint to umount.crypt.

       -r     Set  up  the loop device (if necessary) and crypto device in read-only mode.  (The mount itself will necessarily also be read-only.)
	      Note that doing a remount using `mount /mnt -o remount,rw` will not make the mount readwrite. The crypto and loop devices will  have
	      to be disassociated first.

       -v     Turn on debugging and be a bit more verbose.

Mount options
       cipher The  cryptsetup  cipher  used  for  the  encrypted  volume.  This option is mandatory.  pmt-ehd(8) defaults to creating volumes with
	      "aes-cbc-essiv:sha256" as a cipher.

       dm-timeout=seconds
	      Wait at most this many seconds for udev to create /dev/mapper/name after calling cryptsetup(8). The default value is 0 seconds.

       fsck   Run fsck on the container before mounting it.

       fsk_cipher
	      The OpenSSL cipher used for the filesystem key.

       fsk_hash
	      The OpenSSL hash used for producing key and IV.

       fstype The exact type of filesystem in the encrypted container. The default is to let the kernel autodetect.

       keyfile
	      The path to the key file. This option is mandatory for "normal" crypto volumes and should not be used for LUKS volumes.

       remount
	      Causes the filesystem to be remounted with new options. Note that mount.crypt cannot switch the underlying loop device (if  applies)
	      or the crypto device between read-only and read-write once it is created; only the actual filesystem mount can be changed, with lim-
	      its. If the loop device is read-only, the crypto device will be read-only, and changing the mount to read-write is impossible.  Sim-
	      ilarly,  going from rw to ro will only mark the mount read-only, but not the crypto or loop device, thus making it impossible to set
	      the filesystem the crypto container is located on to read-only.

       ro     Same as the -r option.

       verbose
	      Same as the -v option.

Obsolete mount options
       This section is provided for reference.

       loop   This option used to set up a loop device, because cryptsetup(8) expects a block device. The option is  ignored  because  mount.crypt
	      can figure this out on its own.

pam_mount							    2008-10-08							    mount.crypt(8)
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