27.05.2020 22:11, Eugene M. Zheganin wrote:
> Hello,
>
>
> I have a ZFS dataset about 10T of actual size (may be more) that I need to
> send over a very laggy connection. So I'm sending it from the shell-script
> that reattempts to send it after a short timeout, retrieving the send token
> first. Like that:
>
> ===Cut===
>
> #!/bin/sh
>
> exitstatus=1
> token=`ssh user@server zfs get receive_resume_token data/reference | grep -v
> SOURCE | awk '{print $3}'`
> while ([ $exitstatus -ne 0 ])
> do
> zfs send -t $token | ssh -C user@server sudo zfs receive -Fus
> data/reference
> exitstatus=$?
> echo "Send interrupted/ended, sleeping for 5 secs."
> sleep 5
> done
>
> ===Cut===
>
> Usually this goes just flawlessly. But this time, due to a low transfer speed
> and a very laggy connectivity, thus resulting in a send time of several
> weeks, I got a problem:
>
> about one reattempt out of 200 fails with a situation when there's no
> snapshot on the receiving side (only an incomplete dataset which is
> definitely smaller than original one), thus meaning that the dataset is
> incomplete, but there's no token on this dataset. This happened already
> twice, each time on a different size.
>
> How can this even be possible ?
>
>
> Recieving side side:
>
> [root@playkey-nas:~]# zfs list -t all
> NAME USED AVAIL REFER MOUNTPOINT
> data 4,67T 20,8T 128K /data
> data/reference 4,67T 20,8T 128K /data/reference
>
> (as you can see there's no snapshot)
>
> Sending side and the snapshot:
>
> [root@san1:/usr/src]# zfs list -t all | grep data/reference@ver2_5917
> data/reference@ver2_5917 44,3G - 7,73T -
zfs(8) manual page tells:
receive_resume_token
For filesystems or volumes which have saved partially-completed state
from zfs receive -s, this opaque token can be provided to zfs send -t
to resume and complete the zfs receive.
Note that /bin/sh does NOT support storing arbitrary opaque data in its
variables in unencoded form.
Maybe sometimes you get token with characters that break such code.
Here is how I encode completely opaque and even binary data when I need to
store in a shell variable:
key=$(command_printing_data | b64encode -r -)
# use binary key later:
echo "$key" | b64decode -r | geli attach -pk - $p
This technique works for any kind of data including special symbols, zero bytes
etc.
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