I had great fun watching the YouTube videos for “The Erlang Master Classes”, at The University of Kent, and typing Erlang code along the way. Go and see for yourself at http://www.kent.ac.uk/elearning/themes/masterclasses.html. Here are some thoughts from prof. Simon Thompson, http://profsjt.blogspot.co.uk/2015/06/the-erlang-mini-mooc-pilot-what-have-we.html.
This is an exercise I made, just to remind myself of how snapshots and clones work in ZFS. Also, how to properly get rid of them when you’re short of diskspace, or the dataset listing is too long, etc.
First, we have the shell script that demonstrates the rise and fall of the initial dataset, and the intermediary snapshots and clones.
#!/bin/sh set -x zfs create zroot/clones zfs list -rt all zroot/clones zfs create zroot/clones/a zfs list -rt all zroot/clones zfs snapshot zroot/clones/a@b zfs list -rt all zroot/clones zfs clone zroot/clones/a@b zroot/clones/b zfs list -rt all zroot/clones zfs snapshot zroot/clones/b@c zfs list -rt all zroot/clones zfs clone zroot/clones/b@c zroot/clones/c zfs list -rt all zroot/clones zfs snapshot zroot/clones/c@d zfs list -rt all zroot/clones zfs clone zroot/clones/c@d zroot/clones/d zfs list -rt all zroot/clones zfs snapshot zroot/clones/d@e zfs list -rt all zroot/clones zfs clone zroot/clones/d@e zroot/clones/e zfs list -rt all zroot/clones zfs promote zroot/clones/b zfs list -rt all zroot/clones zfs promote zroot/clones/c zfs list -rt all zroot/clones zfs promote zroot/clones/d zfs list -rt all zroot/clones zfs promote zroot/clones/e zfs list -rt all zroot/clones zfs destroy -v zroot/clones/a zfs list -rt all zroot/clones zfs destroy -v zroot/clones/b zfs list -rt all zroot/clones zfs destroy -v zroot/clones/c zfs list -rt all zroot/clones zfs destroy -v zroot/clones/d zfs list -rt all zroot/clones zfs destroy -v zroot/clones/e@b zfs list -rt all zroot/clones zfs destroy -v zroot/clones/e@c zfs list -rt all zroot/clones zfs destroy -v zroot/clones/e@d zfs list -rt all zroot/clones zfs destroy -v zroot/clones/e@e zfs list -rt all zroot/clones zfs destroy -v zroot/clones/e zfs list -rt all zroot/clones zfs destroy -v zroot/clones
I bought the ebook edition of FreeBSD Mastery: ZFS this June. While the authors’ intentions are good, the 2015-05-21 edition has some errors and mistakes. The table below is nothing more than an unofficial errata of said book. Beware, what you find below might be due to my lack of understanding FreeBSD, ZFS, or the English language.
BTW, if you print this ebook as a booklet using Adobe Reader or similar software, specify a custom range of 1,11,2-234. This trick creates a blank page after the cover page, and places the titlepages and the first page of each chapter on the right side of the sheet. In addition, I had to specify portrait orientation and no auto-rotate. Otherwise the front and back of each sheet would be rotated by 180 degrees. Imagine reading such a book(let).
|10-11||“GPT labels have a maximum length of 15 characters, so you might have to truncate long serial numbers.“
GPT labels are not limited to 15 characters. Nor does FreeBSD limit GPT labels to 15 characters. Such labels are limited to 36 UTF16LE encoded characters (72 octets). Beware,
|17||“Look at the second entry, named
In this case,
|33||“Traditional RAID let you combine multiple disks into one virtual disk, permitting the creation of massive disks as large as 100 MB, or even bigger!“
A virtual disk of 100 MB has been easy for many years. Today, most (physical) disks range from 128 GB to 3 TB. Let’s scale the number up to 100 TB.
|69||“Every zpool retains a copy of all changes that have ever been made to the pool, all the way back to the pool’s creation.“
Yes and no. It depends on how much activity you have in the pool. If you create (and possibly destroy) snapshots regularly, then those commands will eventually fill up the history, and all records of the initial commands will be gone. Maybe this has changed in recent versions of FreeBSD and/or ZFS, but I doubt it.
|80||“You can show filesystems, volumes, or snapshots.“
The list must be extended to include bookmarks, unless this is material for “FreeBSD Mastery: Advanced ZFS”.
|84||A source will be set to
I can’t make sense of the second and the third sentence of the last paragraph on page 114. I suggest a rewrite: “With
|154-159||I’m missing a discussion on the
- Download the required updates.
- Extract the
- Transfer the
XS*.xsupdatefiles to, say,
/tmp/xsupon the master.
- Login on the XenServer console.
- Delete old log files in
- Create if necessary, and change directory to
uuidlist=`for f in XS*; do xe patch-upload file-name=$f; done`
for u in $uuidlist; do xe patch-pool-apply uuid=$u; done
- Delete the
- Shutdown the running VMs and restart each node.
If you want to free some disk space by removing old patches, try:
for p in `xe patch-list --minimal | tr , ' '`; do xe patch-destroy uuid=$p; done
Note, this will also remove any pending or unapplied patches.
Also, make sure you give XenServer more than 4 GiB of disk space to
dom0 when installing the system, preferably 8 GiB or even 10 GiB.
Jeg har lagt merke til at flere bruker ordet «autorativ» der jeg vil bruke ordet «autoritativ». Jeg har lest flere steder om «autorativ DNS-tjener» og lignende, men jeg ville ha skrevet dette som «autoritativ DNS-tjener».
A colleague came into my office claiming the camera in his Dell Latitude E5540 didn’t work. Here’s a link to the Dell Latitude E5540 Owner’s Manual.
After a bit of troubleshooting, I removed the display bezel. Lo and behold, the camera connector was halfway out of its socket. Once I pressed the connector into place, the camera immediately started working. But only after a few seconds the connector dislodged again, and Skype/Windows didn’t detect any camera.
I removed the display, rearranged the camera’s flat cable to lessen the stress, and reconnected the connector. As I began to fasten the display, the camera lost its connection again. Apparently, the socket is slightly too wide or the connector is slightly too narrow, or maybe both, and they slip easily apart.
I removed the display again. I reconnected the camera connector one final time and applied a drop of super glue of the kind I use for security markings. While the glue dried, the camera kept working. After 10 minutes or so, I reattached the display and the display bezel, and the camera was still working. Successful surgery!