Testing glusterfs on centos

Following along the CentOS howto using Centos 7.2

Just a couple of things have changed since it was written:

  1. As per the CentOS storage special interest group, you can now get the glusterfs packages without using wget to retrieve additional repos:
    yum install centos-release-gluster
    
    yum install glusterfs-server samba
  2. Evidently xfs filesystems should be formatted to inode size 512 bytes, not 256.
  3. If you want to delete a volume immediately after creating, you’ll need some incantations to re-use the bricks without re-formating them.

Along the way I asked myself the following questions

  1. Should each of the physical disks be surfaced as a separate volume group and allocated within a single logical volume using 100% of the VG? Allocating 100% prevents using LVM snapshots, but why would you ever want to do that (or is that a building block for GlusterFS snapshots?)  Is there something that could be done to use HSM and LVM to balance blocks on each node?
  2. What is the best filesystem for the bricks? XFS is the default. As above, it should be formatted with 512 byte inodes.
  3. What should the network segmentation and firewall zone configuration be?
  4. What brick layout, replica setting and stripe setting makes sense? The number of bricks are required to be the product of the number of replicas and stripes.
  5. How to best utilise SSD
    1. Through glusterfs file level tiering in the March gluster / Redhat storage tech preview? This version also allows access to erasure coding, lowering the cost of storage replication.
      1. immediately available in the Centos 7.2 build. BUT… works at the file level, so not so helpful with VMs. However if sharding is turned on, perhaps it works at the shard level?
    2. Through block level management with dm-cache or similar, preferably integrated to LVM?
    3. Through hardware RAID controller?
Posted in IT

Cropping multiple images with Gimp and script-fu

I recently had a series of video screenshots from a Gotomeeting screencapture. The presenter screen had resolution 1366×768; the meeting organiser 1920×1080.

The result was that all the images were surrounded with a black border. In turning the screencapture into a set of stills to represent as narrated video, I used the following in Gimp

  • Start Gimp and enter Filters | Script-fu | Console
  • In the console that comes up, paste the following to define the batch-resize function
(define (batch-resize pattern
                      new-width
                      new-height
                      offx
                      offy)
(let* ((filelist (cadr (file-glob pattern 1))))
 (while (not (null? filelist))
        (let* ((filename (car filelist))
        (image (car (gimp-file-load RUN-NONINTERACTIVE
                                    filename filename)))
        (drawable (car (gimp-image-get-active-layer image))))
        (gimp-layer-resize drawable new-width new-height offx offy)
        (gimp-image-resize-to-layers image)
        (gimp-file-save RUN-NONINTERACTIVE
                        image drawable filename filename)
        (gimp-image-delete image))
        (set! filelist (cdr filelist)))))

  • Then in the same console you can run the following
(batch-resize "/path/to/screenshots/*png" 1366 768 -272 -157)

Note that this was on a windows system – and the format of the filesystem path is still with forward slash. Note also, this will replace existing files with modified versions.

If you want to perform some other form of processing on each file, the key function to replace is (gimp-layer-resize …)

Form more information, see the Script-fu Tutorial or the Gimp scripting manualIT

Posted in IT

The dangers and opportunities of statistical multiplexing gain

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Evidently Sandringham used to be served by first a house drawn, and then an electric, tram. The horse drawn services were wound up in 1914 as “The cost of keeping horses for these peak [holiday] times led to the demise of the Company’s services”.

Telco profits often stem from statistical multiplexing gains – sell 1000 x 10 Mbps user services, provision only 500 Mbps backhaul. Beware, though, if you have service level obligations in peak periods and have high peak to average demand statistics.

Ref. Rotary Club of Sandringham bus shelter display on Bay Rd.

Home again

 

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Somewhat symmetrically… back at southern cross for sunrise. Turns out our fellow passenger from London was also catching the Sandringham line, we meet him again on the platform.

Dolphins! On the bay past Brighton Beach. Good to be home.

Bristol Street Art

Bristol Street Art Tours – although we could have walked the streets of Bristol for free and seen these amazing works, we wouldn’t have had a window into the other world that street artists inhabit.  Our guide opened up the complexity of practicing street art – legality vs illegality, tourism, technical production, attitudes from city authority, impermanence,  the inter-generational conflict, digital archiving and promotion, and international participation in the recent historical context.

I was so good, I didn’t mind it was 12 degrees and raining.

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BTW, the guide did cover Banksy, too.

Bristol – Squirrels around Cabot Tower

The squirrels around Cabot tower are obviously hand-fed; they come hunting around to see if you will feed them. In this case, the squirrel wanted to see if the camera was edible. The grey squirrel is an invasive species in the UK; the red squirrel it is displacing was signposted in a number of places in the Lake District (including one notable 20% gradient and squirrel alert sign), but we failed to spot any.

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SS Great Britain

The SS Great Britain is one of the first hybrid steam driven screw/sail power iron construction ocean going ships. Built in Bristol in the mid-1800s, it was scuttled in the Falkland Islands in the 1930s. It was then salvaged in the 1970s and returned, with the dry-dock used to construct it retired by receiving the recovered vessel and being converted into a museum conserving the ship.

The most unusual thing I found out from the exhibition, is that the ship was later converted to have a retractable prop to allow pure sail driven locomotion. In the late 1800s they were trying to save money in the cargo freight business by avoiding burning coal!

The displays seem to be dumbed down a little and would be quite accessible to a younger audience, at the cost of drawing you into the engineering details and illustrating Brunel’s mastery.

The olfactory component of the ship kitchen and bakery exhibits was a nice touch.

All in all, a good experience.

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Bristol

Transit time from Australia to Bristol via Dubai and Heathrow, courtesy of Metrotrains, Skybus, Qantas and National Express was around 32 hours including all transfers. While Danielle had been around here for a week visiting Ben, I spent only spent two nights in Clifton. Nearby attractions include Cabot Tower, SS Great Britain, and the Brunel Suspension Bridge.

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houses in Clifton, Bristol

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Bristol panorama from Cabot Tower.

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Ducks, in the water labyrinth beneath Cabot Tower

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Strawberry clover, beneath Cabot Tower

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Meadow inspection, beneath Cabot Tower

Brunel Suspension Bridge.

Brunel Suspension Bridge.

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Bristol Railway Station Art Installation – Aluminium on Brick

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Bristol Railway Station – Art Installation. We are becoming digitised?

Llangollen

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Today brought us through wonderful Welsh countryside to Llangollen. The river Dee rushes past the old corn mill, now a pub, and steam trains run on the other side of the river.

The pub celebrates the history of trap shooting.

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Chirk and the local nobility

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Today we’ve arrived in Chirk. Transferring train at Newport was like arriving in a foreign european country – not the mother country like Bristol. All the station signs were bilingual. The train through the Welsh country side was lovely. On arrival at Chirk, we walked across to the hotel, puzzling about the sweet smell in the air. Turns out that a chocolate factory opened here around 1967, as we found later from a local.

The Hand Hotel, Chirk (pictured), four centuries old, was owned by the local Myddleton family until 1911. The Myddleton’s had also owned the local castle (constructed in Norman times) since the 1600s.

After eating lunch at The Hand and then checking in, we checked out where to buy provisions in the morning (including the butcher’s 6 varieties of bacon), and then started a walk up the hill to the castle. The walk through meadows and farm land was lovely.

The castle is now owned or long term leased by the National Trust, but one wing is still inhabited by the Myddleton family. The surrounding farming operation seemed to have been outsourced / agisted over the past century. The bus driver for the national trust shuttle to the car park kindly gave us a lift home at the end of the day. He told us how his grandparents and father had worked on the estate most of the 1900s.