Using loopback devices in RAID?


 
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Special Forums Hardware Filesystems, Disks and Memory Using loopback devices in RAID?
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Old 04-16-2003
Question Using loopback devices in RAID?

Hopefully I am posting this silly question in the right place...

I was wondering about the possibility of using loopback files on a physical disk to create virtual disks that could shrink or grow as needed. Something like RAID 0, but instead of using block devices, just using files. If I need more space, I just add another loopback file to the pool. If I don't need it anymore, I just remove it. But doing either of these things doesn't damage the data. Does anyone know if this is possible?

Similarly, I was also wondering is it's possible to mount multiple NFS or Samba shares to one location and have them all appear as a single "mounted device". For instance, if I want to mount th C$ share on an NT box and 10.0.1.1:/home on /mnt/files. Is there a way to do this?

Thanks.
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raidstart(8)						      System Manager's Manual						      raidstart(8)

NAME
raidstart, raidstop, - command set to manage md devices. SYNOPSIS
raidstart [options] <raiddevice>* raidstop [options] <raiddevice>* DESCRIPTION
RAID devices are virtual devices created from two or more real block devices. This allows multiple disks to be combined into a single filesystem, possibly with automated backup and recovery. Linux RAID devices are implemented through the md device driver. If you're using the /proc filesystem, /proc/mdstat gives you informations about md devices status. Currently, Linux supports linear md devices, RAID0 (striping), RAID1 (mirrroring), and RAID4 and RAID5. For information on the various lev- els of RAID, check out: http://ostenfeld.dk/~jakob/Software-RAID.HOWTO/ for new releases of the RAID driver check out: ftp://ftp.fi.kernel.org/pub/linux/daemons/raid/alpha Avaible commands are : mkraid : configures (creates) md (RAID) devices in the kernel, banding multiple devices into one. raidstart : activates (starts) an existing 'persistent' md device raid0run : activates old nonpersistent RAID0/LINEAR md devices raidstop : turns off an md device, and unconfigures (stops) it By default, a systems RAID configuration is kept in /etc/raidtab, which can configure multiple RAID devices. All of these tools work similiarly. If -a (or --all) is specified, the specified operation is performed on all of the RAID devices men- tioned in the configuration file. Otherwise, one or more RAID devices must be specified on the command line. For example: raid0run -a Starts all of the 'old' RAID0 RAID devices specified in /etc/raidtab. If only /dev/md1 should be started, the following command should be used instead: raidstart /dev/md1 OPTIONS
-a, --all Apply the command to all of the configurations specified in the config file. -c, --configfile filename Use filename as the configuration file (/etc/raidtab is used by default). -h, --help Displays a short usage message, then exits. -V, --version Displays a short version message, then exits. NOTES
The raidtools are derived from the md-tools and raidtools packages, which were originally written by Marc Zyngier, Miguel de Icaza, Gadi Oxman, Bradley Ward Allen, and Ingo Molnar. BUGS
no known bugs. SEE ALSO
raidtab(5), raid0run(8), raidstop(8), mkraid(8) raidstart(8)