sabi notesNotes mostly about Linux and computer issuessabicohttp://www.sabi.co.uk/Copyright 2014 Peter G.http://www.sabi.co.uk/2015-12-16T21:05:00ZIPsec and VLANs2014-12-26T12:20:00Z2014-12-26T12:20:00Zhttp://www.sabi.co.uk/blog/141226IPsec can be used just to implement
Virtual Private Links between two hosts, but when used
properly to implement Virtual Private Networks among many
hosts that can replace VLANs for traffic segregation, with
numerous advantages; the disadvantage of higher CPU use is
largely obviated by AES hardware acceleration and the
routine availability with systems with many CPUs.IPsec possibilities and realities2014-12-11T21:00:00Z2014-12-11T21:00:00Zhttp://www.sabi.co.uk/blog/141211IPsec was designed for multilateral
end-host to end-host private communications, but it has been
used almost only for bilateral private communications
between subnet gateways. Unfortunately this is also the
result of the misdesign of popular IPsec implementations
that focus on links instead of nodes. Some examples given of
how to write typical IPsec configurations, including a
workaround that almost allows multilateral node-based
configurations using SSH RSA host keys that are already
present on most systems.Slicing across large disks versus slicing many disks2014-11-28T12:15:00Z2014-11-28T12:15:00Zhttp://www.sabi.co.uk/blog/141128Large RAID virtual block devices can be
create with many smaller disks or a few larger disks. Given
that single larger storage pools are rarely necessary the
many smaller disks can be sliced "longitudinally" into
several smaller subsets. This cannot be done directly for
the low IOPS per TB case of a few larger disks, and
therefore a second-best option is to partition the larger
disks and make multiple RAID sets of those partitions,
slicing the disk set capacity "latitudinally".Rack and rack row layout2014-11-27T18:45:00Z2014-11-27T18:45:00Zhttp://www.sabi.co.uk/blog/141127For some reasons a lot of rack layouts
cluster together devices by type. This usually creates tidy
looking racks but very untidy and tangled cabling and
increases the risks of wider impact of issues. It seeems
much better to me to use as guideline minimizing cable
lengths, putting highly connected equipment in the middle of
the other equipment they are connected to, and so for
example put front-end servers in the top third of a rack,
switches an patch panels in the middle third, and storage
servers in the bottom third.Advantages and disadvantages of IPS and VA panels2014-11-26T21:20:00Z2014-06-28T18:40:00Zhttp://www.sabi.co.uk/blog/140628Comparison of advantages and
disadvantages of IPS and VA panels. On most aspects IPS
panels are slightly or somewhat better except on contrast
where VA panels are much better because of deeper
blacks.3GB of pending writes and 'umount' takes time2014-11-20T21:50:00Z2014-10-10T19:50:00Zhttp://www.sabi.co.uk/blog/141010Having 3GB of uncommitted storage
updates in memory is usually a bad idea even outside the
case where there is a high latency slow link between the
computer and the storage device, especially with Linux
and/or many types of storage HA that have inappropriate
scheduling or caching policies.Amazing 32-wide RAID5 performs as expected2014-10-19T10:30:00Z2014-10-19T10:30:00Zhttp://www.sabi.co.uk/blog/141019A 100TB RAID5 set has very low
concurrent read-write speed. It seems to have 32 member
disks of 3TB, which would imply massive RMW issues. Plus it
seems built from a hw RAID HA, and many have significant
misdesigns as to scheduling concurrent accesses of different
types. Overall a RAID5 set of 32 members like that has some
rather undesirable properties for most workloads, except
one: it has the lowest upfront cost, and that is what often
matters most.Rediscovered old 17in LCD monitor comparison2014-11-01T10:20:00Z2014-11-01T10:20:00Zhttp://www.sabi.co.uk/blog/141101Had a look at a 17in monitor bought in
2003 and it still feels quite usable, even if the backlight
has become yellower and dimmer with time. But even cheap
contemporary monitors are much better, mostly thanks to
developments targeted at LCD television screens.Resizing images needs gamma handling, and monitor testing2014-09-21T11:30:00Z2014-09-21T11:30:00Zhttp://www.sabi.co.uk/blog/140921Gamma handling is subtle, and an
article shows that resizing images must be done in linear
colorspace, not gamma adjusted, to avoid intensity
distortion, and that most current image editing program
don't. The article also contains sample images that work
well to test gamma and color settings of monitors.My current desktop PC components2014-09-23T18:10:00Z2014-09-23T18:10:00Zhttp://www.sabi.co.uk/blog/140923I have recently upgraded my main
desktop system, and I have also setup a while ago a nice
gaming/test system, and I describe their main components
and some general considerations on my choices.ECC motherboards and memory for ordinary computers2014-09-19T19:30:00Z2014-09-19T19:30:00Zhttp://www.sabi.co.uk/blog/140919It is still possible to get
consumer-style CPUs and motherboards that support ECC
memory, in particular with ADM CPUs and ASUS motherboards,
and ECC memory is not much more expensive than parity-less
memory.Firefox memory usage increase and restarting2014-09-22T17:40:00Z2014-09-22T17:40:00Zhttp://www.sabi.co.uk/blog/140922AJaX pages can grow very large, and
even when closed most of the associated memory continues to
be in use. The most effective way to release what is
effectively unused memory is to restart Firefox, and the
most convenient way seems to be to use two extensions.MH-style mail archives, VCS archives, log-like data2014-08-28T14:00:00Z2014-08-28T14:00:00Zhttp://www.sabi.co.uk/blog/140828In general storing records of a
collection as individual files in a directory structure is a
bad idea because files are defined by most filesystem APIs
as heavyweight entities. So storing archives that ways is
particularly inappropriate. It is more appropriate for
spools, where individual members odf the collection are
added and removed randomly, and the collection is usually
fairly small. Using files for storing individual records is
inappropriate not just for archives, but also for
collections organized timewise where most active records are
the most recent ones and records are rarely deleted, which
includes most collections of data related to people's life
and work, with the significant but partial exception of
program source and object files under active
development.Amazing shrink of Xapian database2014-08-31T22:50:00Z2014-08-31T22:50:00Zhttp://www.sabi.co.uk/blog/140831The local search engine 'recoll' uses
Xapian as a database and by default it uses B-trees. Using
a tool to compact freshly filled Xapian databases is not
unexpectedly quite effective.Still happy with Dell U2412M and Acer B326HUL2014-08-29T22:20:00Z2014-08-29T22:20:00Zhttp://www.sabi.co.uk/blog/140829Still quite impressed with the Dell
U2412M IPS 24in monitor and the Acer B326HUL AMVA 32in
monitor.Flies and LCD monitors2014-08-03T11:10:00Z2014-08-03T11:10:00Zhttp://www.sabi.co.uk/blog/140803Hot weather means open windows and
flies come in and are attracted to my LCD display and leave
droppings.Some impressions of high-end pointer devices2014-08-01T19:40:00Z2014-08-01T19:40:00Zhttp://www.sabi.co.uk/blog/140801My impressions of three high-end mice,
the Corsair Raptor M40, the Zowie EC1, the Mionix NAOS 3200
and two high-end mousepads, the Mionix ENSIS 320 and the 3M
Precise Mousing Surface.Why pay more for premium keyboards2014-07-15T20:50:00Z2014-07-15T20:50:00Zhttp://www.sabi.co.uk/blog/140715The main advantage of premium keyboards
is not that they have mechanical key switches, because some
don't, but that they use springs instead of rubber domes.
Other advantages are secondary but also interesting, such
as better build quality and wider range of options.Xorg, Ubuntu, 'radeon' driver work well on AMD GPUs2014-07-11T23:55:00Z2014-07-11T23:55:00Zhttp://www.sabi.co.uk/blog/140711With Linux 3.13 packages and other
backports from Ubuntu 14.04 games like Team Fortress 2 run
at speed comparable to that under MS-Windows in AMD/ATi
cards like the older 4770 and the newer 7850, which is a
great achievement.Evaluation of some more high end keyboards2014-07-10T19:10:00Z2014-07-10T19:10:00Zhttp://www.sabi.co.uk/blog/140710Impressions of the Ducky 9087 TKL
keyboard with Cherry MX Black key switches, and of the Ducky
set of engraved PBT keycaps for Cherry MX key switches. The
keyboard is very good but with pointless features, and the
keycaps are of excellent quality but expensive and don't
have colored legends, which makes them sometimes hard to
read.Evaluation of some high end keyboards2014-07-04T21:00:00Z2014-07-04T21:00:00Zhttp://www.sabi.co.uk/blog/140704Inmpressions of two mechanical
keyboards, the CM QuickFire TK Stealth with back-captioned
keycaps, and the Corsair Vengeance K65, also TKL; both with
an unusually low price for mechanical keyboards. They are
both pretty good, even if the back-printed keycaps are only
readable in good conditions and the K65 has low end sticker
captions. But they are cheap enough that buying an
additional premium keycap set is feasible.Firefox color preference disabled background images2014-06-28T14:10:00Z2014-06-08T11:30:00Zhttp://www.sabi.co.uk/blog/140608For some deliberate but disagreeable
reason the Firefox preference that forces user color choices
also disables background images, even if background images
are often essential as they are widely misused instead of
the 'img' element to display images.Impressions of the Acer B326HUL 32in monitor2014-06-24T18:40:00Z2014-06-24T18:40:00Zhttp://www.sabi.co.uk/blog/140624The B326HUL has a very recent 32in
2560x1440 VA panel with excellent contrast, good colors and
viewing angles, and a good mechanical design, and is also
much cheaper than a 30in monitor.Updated traffic shaping script2014-06-10T13:15:00Z2012-08-20T00:55:00Zhttp://www.sabi.co.uk/#sourcesSabishape?120819I have updated my Linux traffic shaping
script. It is a very small update but fixes a significant mistake
with some kernel versions.Big changes in Ubuntu and online game stores2014-04-05T12:00:00Z2014-04-05T12:00:00Zhttp://www.sabi.co.uk/blog/140405Canonical suddendly cancel the U1
service, and Amazon introduce a game console with an online
game store competiting with Steam. The first demonstrates
how fleeting some products can be, the second will motivate
Valve Software to be even more committed to SteamOS.SteamOS may become a significant server Linux distribution2014-03-26T19:30:00Z2014-03-19T20:00:00Zhttp://www.sabi.co.uk/blog/140319SteamOS is very strategic for its
sponsor, long term, and might end up installed on dozens of
millions of systems. This might expose to a wide variety of
issues and elicit a strong level of investment in
maintainability from its sponsor, and make it a desirable
hardened distribution for servers. Just potentially, but
worth watching.Route metrics and address subnet prefixes2014-03-26T08:40:00Z2014-03-26T08:40:00Zhttp://www.sabi.co.uk/blog/140326Because of some limitation in the Linux
IP implementation it is preferable to configure network
interfaces with separate IP address and route to the
relevant subnet than use the combined syntax for both
address and subnet.Icinga and getting rid of PHP2014-03-24T20:30:00Z2014-03-24T20:30:00Zhttp://www.sabi.co.uk/blog/140324I found that some packages I had
installed and not removed still required PHP, and if I
removed them and installed instead of Nagios3 its fork
Icinga which does not depend on PHP I could remove
it.Apple re-defines the unit of measure 'point'2014-03-22T11:00:00Z2014-03-12T20:20:00Zhttp://www.sabi.co.uk/blog/140312Apple on iOS have felt the need to
create a floating point coordinate system for graphics and
text and its unit of measure for position is called "point",
redefining a term used for centuries the unit used for the
size of printed characters.Replacing 'loop-AES' with 'dm-crypt'2014-03-18T21:10:00Z2014-03-18T21:10:00Zhttp://www.sabi.co.uk/blog/140318Regrettably the storage encryption
driver 'loop-AES' has not yet been updated for recent kernel
versions; the lesser alternative driver 'dm-crypt' has been
extended with 'loop-AES' compatibility, and being in-kernel
it gets updated, so it can replace 'loop-AES' without having
to reconstruct the storage areas previously encrypted with
'loop-AES'.Packages for Steam on Debian 7/Wheezy2014-03-17T22:10:00Z2014-03-17T22:10:00Zhttp://www.sabi.co.uk/blog/140317A detailed list of which packages to
get and how to get them from the SteamOS repositories to
allow a mostly-standard Debian 7/Wheezy to run the Steam
game downloader and its games well.Packages for Steam on Ubuntu LTS 12.042014-03-15T11:00:00Z2014-03-18T19:50:00Zhttp://www.sabi.co.uk/blog/140315A detailed list of which packages to
get and how to get them for updating a mostly-standard
Ubuntu LTS 12.04 systems to run the Steam game downloader
and its games well.DPI, viewing distance and font glyph sizes2014-02-28T09:10:00Z2014-02-28T09:10:00Zhttp://www.sabi.co.uk/blog/140228Text has been traditionally set at 10
points, because that is good for normal reading distance,
usually a forearm away from the eyes. But currently the
displays of laptops are viewed from an arm's length when the
laptop is on the user's knees, and large desktop monitors
also are viewed from an arm's length to be able to take in
their full surface, This causes problems because at an arm's
length text should be scaled to be bigger. This is not
something current windowing systems and HUI applications do
well.Kerberos tickets, addresses, forwarding, SSH2014-01-11T10:30:01Z2014-01-11T10:30:00Zhttp://www.sabi.co.uk/blog/140111OpenSSH can delegate security
credentials from the source to the target hosts. However
when delegating Kerberos tickets a confusion is made between
forwardable tickets and delegated tickets, which results in
some pointless wider consequences in case of compromises of
the target host. Some example is given.HGST 4TB archival storage disk drive profile2014-01-04T16:10:00Z2014-01-04T16:10:00Zhttp://www.sabi.co.uk/blog/140104HGST have introduced a 4 GB disk drive
for archivel storage which has a rating for total lifetime
traffic, somewhat unusual for disk drives.