This tool allows you to image an actively changing block device. Including the one the rootfs is stored on.
hot-clone uses blktrace, and needs root to enable it. Performance impact seems to be low, though if you are planning to image a highly loaded disk you will want to change the values of:
-blktrace.bufcount int
The amount of buffers for blktrace to keep spare (default 16)
-blktrace.bufsize int
The size of each buffer for blktrace (default 65536)
To something higher, Ideally not too high since it will add latency to disk change events.
$ sudo ./hot-clone -device /dev/sdb > sdb.hc
[sudo] password for ben:
2021/09/19 22:36:27 Read 18.0 MiB -- 0 Dirty sectors (0 event drops)
...
2021/09/19 22:39:48 Read 3.7 GiB -- 360 Dirty sectors (0 event drops)
2021/09/19 22:39:49 Catching up 36/360 sectors
2021/09/19 22:39:49 Catching up 72/360 sectors
2021/09/19 22:39:49 Catching up 108/360 sectors
2021/09/19 22:39:49 Catching up 144/360 sectors
2021/09/19 22:39:49 Catching up 180/360 sectors
2021/09/19 22:39:49 Catching up 216/360 sectors
2021/09/19 22:39:49 Catching up 252/360 sectors
2021/09/19 22:39:49 Catching up 288/360 sectors
2021/09/19 22:39:49 Catching up 324/360 sectors
2021/09/19 22:39:49 Catching up 360/360 sectors
2021/09/19 22:39:49 Done
The output it piped to stdout, this is so you can output to a file or a pipe (or directly invoke it from ssh)
You cannot directly restore the output of hot-clone, you will first need to reassemble it. To do this you select -reassemble for the hot-clone output, and -reassemble-output to the device or file you wish to restore to.
$ ./hot-clone -reassemble sdb.hc -reassemble-output sdb.img
2021/09/19 22:40:14 Restoring section (Sector: 0 (len 3959422976 bytes)
$
Golang 1.13 or later is needed to compile. Debian 11 has a reccent enough version, compiling on older Debian will require manually installing golang.
Compiling on Debian 11 and copying the executable to a box running an older OS seems to work (on 64bit PC hardware).
To compile an executable binary:
On the github page, click on code, click on "Download ZIP".
$ unzip -e hot-clone-main.zip
$ cd hot-clone-main
$ go build
See if your executable runs.
$ ./hot-clone --help
-blktrace.bufcount int
The amount of buffers for blktrace to keep spare (default 16)
-blktrace.bufsize int
The size of each buffer for blktrace (default 65536)
-device string
The device you wise to hot-clone
-print-writes
print all writes happening
-reassemble string
use this hot-clone backup file to restore into a file or block device
-reassemble-output string
The path of the file or block device that is going to be restored to
-verbose
be extra verbose on whats happening
Brief testing indicates that this works on Debian 8, 9, 10 and 11 and Ubuntu 18.10.
Debian 7 does not have the TRACE interface so hot-clone won't work.
You should avoid using this tool if you can help it. LVM, MD Raid, and DRBD give you far better (and tested) methods to enable system snapshotting/real time backups.
