If I have a sparse file representing a block device, then how can I efficiently restore the file over a network? Ideally, I'd use rsync -S host:file /dev/sdb, but rsync won't write to block devices. I am using ssh host dd if=file | dd of=/dev/sdb, but that's not efficient as the zero bytes will come over the network and be written to the device. Can I use tar -S or cp --sparse=always somehow? Can I do this without storing the file locally (even temporarily)? Can sshfs recognise sparse files?
Asked
Active
Viewed 2,004 times
5
Jayen
- 211
3 Answers
3
I haven't tested it, but there is a write-devices patch to rsync, which would solve your problem. You can find the patch in the rsync-patches repository.
Oliver
- 131
2
You can install the iSCSI Enterprise Target software and setup an iSCSI LUN from the sparse-file like so:
In /etc/iet/ietd.conf:
Target iqn.my.iscsi.test:disk1
Lun 0 Path=/path/to/my/sparse_file,Type=fileio
Then initiate the target from the host you need to restore on. Since the target will show as a local device (eg. /dev/sdd), you can dd from that device to your local device.
Tim
- 6,141
-
1How is this more efficient then what I have now? Once I use dd, won't it read and write the zero bytes? – Jayen Aug 03 '12 at 22:50
-
No more hassle from "middle man" programs. – Tim Aug 07 '12 at 16:01
0
Have you tried compressing/decompressing the data in flight? Batches of zeroes should compress well.
Actually, having thought about it again, it's very simple. On the remote host, create a pipe with mkfifo. scp/dd to that pipe as usual and cp --sparse=always from it to the actual target file.
Tested on my installation and it does produce a sparse file on output. Thanks for a nice question!
Karol Nowak
- 136