Tag: Linux

MegaCLI: useful commands

Posted on by Frederik

Recently I installed a server with a Supermicro SMC2108 RAID adapter, which is actually a LSI MegaRAID SAS 9260. LSI created a command line utility called MegaCLI for Linux to manage this adapter. You can download it from their support pages. The downloaded archive contains an RPM file. I installed mc and rpm on Debian with apt-get, and then extracted the MegaCli64 binary (for x86_64) to /usr/local/sbin, and the libsysfs.so.2.0.2 from the Lib_utils RPM to /opt/lsi/3rdpartylibs/x86_64/ (that’s the location where MegaCli64 looks for this library).

Here are some useful commands:

View information about the RAID adapter

For checking the firmware version, battery back-up unit presence, installed cache memory and the capabilities of the adapter:

# MegaCli64 -AdpAllInfo -aAll

View information about the battery backup-up unit state

# MegaCli64 -AdpBbuCmd -aAll

View information about virtual disks

Useful for checking RAID level, stripe size, cache policy and RAID state:

# MegaCli64 -LDInfo -Lall -aALL

View information about physical drives

# MegaCli64 -PDList -aALL

Patrol read

Patrol read is a feature which tries to discover disk error before it is too late and data is lost. By default it is done automatically (with a delay of 168 hours between different patrol reads) and will take up to 30% of IO resources.

To see information about the patrol read state and the delay between patrol read runs:
# MegaCli64 -AdpPR -Info -aALL

To find out the current patrol read rate, execute
# MegaCli64 -AdpGetProp PatrolReadRate -aALL

To reduce patrol read resource usage to 2% in order to minimize the performance impact:
# MegaCli64 -AdpSetProp PatrolReadRate 2 -aALL

To disable automatic patrol read:
# MegaCli64 -AdpPR -Dsbl -aALL

To start a manual patrol read scan:
# MegaCli64 -AdpPR -Start -aALL

To stop a patrol read scan:
# MegaCli64 -AdpPR -Stop -aALL

You could use the above commands to run patrol read in off-peak times.

Migrate from one RAID level to another

In this example, I migrate the virtual disk 0 from RAID level 6 to RAID 5, so that the disk space of one additional disk becomes available. The second command is used to make Linux detect the new size of the RAID disk.

# /usr/local/sbin/MegaCli64 -LDRecon -Start -r5 -L0 -a0
# echo 1 > /sys/block/sda/device/rescan

Extending an existing RAID array with a new disk

./MegaCli64 -LDRecon -Start -r5 -Add -PhysDrv[32:3] -L0 -a0

Create a new RAID 5 virtual disk from a set of new hard drives

First we need to now the enclosure and slot number of the hard drives we want to use for the new RAID disk. You can find them out by the first command. Then I add a virtual disk using RAID level 5, followed by the list of drives I want to use, specified by enclosure:slot syntax.

# MegaCli64 -PDList -aALL | egrep 'Adapter|Enclosure|Slot|Inquiry'
# MegaCli64 -CfgLdAdd -r5'[252:5,252:6,252:7]' -a0

Extending an existing RAID array with a new disk

First check the enclosure device ID and the slot number of the newly added disk with the command above. Then we reconstruct the logical drive, adding the new drive. For a RAID 5 array this command is used:

# MegaCli64 -LDRecon -Start -r5 -Add -PhysDrv[32:3] -L0 -a0

View reconstruction progress

When reconstructing a RAID array, you can check its progress with this command.
# MegaCli64 -LDRecon ShowProg L0 -a0

(replace L0 by L1 for the second virtual disk, and so on)

Configure write-cache to be disabled when battery is broken

# MegaCli64 -LDSetProp NoCachedBadBBU -LALL -aALL

Change physical disk cache policy

If your system is not connected to a UPS, you should disable the physical disk cache in order to prevent data loss.

# MegaCli -LDGetProp -DskCache -LAll -aALL

To enable it (only do this if you have a UPS and redundant power supplies):

# MegaCli -LDGetProp -DskCache -LAll -aALL

More information

http://ftzdomino.blogspot.com/2009/03/some-useful-megacli-commands.html
https://twiki.cern.ch/twiki/bin/view/FIOgroup/DiskRefPerc
http://hwraid.le-vert.net/wiki/LSIMegaRAIDSAS
http://kb.lsi.com/KnowledgebaseArticle16516.aspx

Fixing grub-probe error: Couldn’t find PV, check your device.map.

Posted on by Frederik

Today I was getting this error when installing a new kernel on a server running Debian:

/usr/sbin/grub-probe: error: Couldn't find PV pv2. Check your device.map.

The error can be reproduce by running the update-grub command.

The day before, a new RAID disk was added to this server, so I suspected this could be the cause. The file /boot/grub/device.map contained a reference to the first RAID disk as (hd0) but did not contain a reference to the new RAID disk. I ran

# ls -l /dev/disk/by-id/

to find out which SCSI ID referred to sdb (the new RAID disk), and then added the following line to device.map:


(hd1) /dev/disk/by-id/scsi-3600304800087c4f015fb4f2e4cc7a8e5

Now installing the new kernel works fine!

Linux performance improvements

Posted on by Frederik

Two years ago I wrote an article presenting some Linux performance improvements. These performance improvements are still valid, but it is time to talk about some new improvements available. As I am using Debian now, I will focus on that distribution, but you should be able to easily implement these things on other distributions too. Some of these improvements are best suited for desktop systems, other for server systems and some are useful for both. Continue reading “Linux performance improvements”

GNOME Shell moving forward

Posted on by Frederik

Some news about GNOME 3 and GNOME Shell:

  • The minimize and maximize window decoration buttons are now removed. It is estimated that these buttons are not useful actually, and users should be using Alt-Tab, the dock or different workspaces to switch between different applications, and maximize windows by double clicking on the title bar. As this will also make the desktop more difficult to access, I guess this also means that there are no plans to re-implement desktop icons.
  • The problem with the ellipsis of long application names has been fixed by enlarging the icons in the application browser.
  • On the -shell IRC channel there was a discussion earlier today about the implementation of shutdown in GNOME Shell. Several developers were in favour of just suspending to RAM by default and not showing a real shut down button by default. After 30 minutes, the system would wake up again and suspend to disk. Several developers did not seem to care about the risks of waking up a laptop while it’s being transported in a bag. Or about the fact suspend is not working properly on all systems.

I am extremely disappointed by these three things. When writing my previous GNOME Shell article, I still had some hopes that things would improve for the better, but I am giving up all hope: the GNOME Shell in GNOME 3.0 will definitely not be something I will like to use. I think it is also unacceptable that such important, drastic changes are made just before or even after the UI freeze. I have the feeling that GNOME Shell is purely the work of a few developers and designers who made some radical changes without any feedback or testing by real end users. The user community seems to be completely forgotten in the GNOME 3.0 development process. As only a few distributions are shipping live CDs, which are often rather unstable and rarely have a completely up to date GNOME Shell, only a very small amount of users is actually able to test and give feedback.

What will I do now? Skip GNOME 3.0 and hope that GNOME 3.2 will be better, once developers have taken into account users reactions? But that means that I will not benefit for more than another 6 months of any improvements to many of my preferred applications. Or use GNOME 3.0 with the old GNOME Panels (but will that give back my desktop icons)? Or shall I finally switch to KDE? Time will tell.

Update: the changes I described here can be seen in screenshots on Webupd8.

Improving Mediawiki performance

Posted on by Frederik

Now that I am on the subject of improving performance, I configured some performance improvements for a Mediawiki installation here:

  • Make sure you run the latest Mediawiki version. Mediawiki 1.16 introduced a new localisation caching system which is supposed to improve performance, so you definitely want this to get the best performance.
  • Create a directory where Mediawiki can store the localisation cache (make sure it is writable by your web server). By preference store it on a tmpfs (at least if you are sure it will be big enough to store the cache), and configure it in LocalSettings.php:
    $wgCacheDirectory = "/tmp/mediawiki";
    Iif /tmp is on a tmpfs, you might add creation of this directory with the right permissions to /etc/rc.local, so that it still exists after a reboot.
  • Enable file caching in Mediawiki’s LocalSettings.php:
    $wgFileCacheDirectory = "{$wgCacheDirectory}/html";
    $wgUseFileCache = true;
    $wgShowIPinHeader = false;
    $wgUseGzip = true;
  • Make sure you have installed some PHP accelerator for caching. I have APC installed and configured it in Mediawiki’s LocalSettings.php:
    $wgMainCacheType = CACHE_ACCEL;

Here is a benchmark before implementing the above configuration (with CACHE_NONE, but APC still installed):

$ ab -kt 30 http://site/wiki/index.php/Page
This is ApacheBench, Version 2.3 < $Revision: 655654 $>
Copyright 1996 Adam Twiss, Zeus Technology Ltd, http://www.zeustech.net/
Licensed to The Apache Software Foundation, http://www.apache.org/

Benchmarking site (be patient)
Finished 255 requests

Server Software: Apache/2.2.16
Server Hostname: site
Server Port: 80

Document Path: /wiki/index.php/Page
Document Length: 12750 bytes

Concurrency Level: 1
Time taken for tests: 30.084 seconds
Complete requests: 255
Failed requests: 0
Write errors: 0
Keep-Alive requests: 0
Total transferred: 3344070 bytes
HTML transferred: 3251250 bytes
Requests per second: 8.48 [#/sec] (mean)
Time per request: 117.978 [ms] (mean)
Time per request: 117.978 [ms] (mean, across all concurrent requests)
Transfer rate: 108.55 [Kbytes/sec] received

Connection Times (ms)
min mean[+/-sd] median max
Connect: 3 6 2.8 7 21
Processing: 88 112 11.1 112 163
Waiting: 66 90 9.1 89 125
Total: 95 118 11.9 118 170

Percentage of the requests served within a certain time (ms)
50% 118
66% 122
75% 125
80% 127
90% 132
95% 138
98% 145
99% 156
100% 170 (longest request)

And here a benchmark after implementing the changes:

ab -kt 30 http://site/wiki/index.php/Page
This is ApacheBench, Version 2.3 < $Revision: 655654 $>
Copyright 1996 Adam Twiss, Zeus Technology Ltd, http://www.zeustech.net/
Licensed to The Apache Software Foundation, http://www.apache.org/

Benchmarking site (be patient)
Finished 649 requests

Server Software: Apache/2.2.16
Server Hostname: site
Server Port: 80

Document Path: /wiki/index.php/Page
Document Length: 12792 bytes

Concurrency Level: 1
Time taken for tests: 30.015 seconds
Complete requests: 649
Failed requests: 0
Write errors: 0
Keep-Alive requests: 0
Total transferred: 8538244 bytes
HTML transferred: 8302008 bytes
Requests per second: 21.62 [#/sec] (mean)
Time per request: 46.248 [ms] (mean)
Time per request: 46.248 [ms] (mean, across all concurrent requests)
Transfer rate: 277.80 [Kbytes/sec] received

Connection Times (ms)
min mean[+/-sd] median max
Connect: 3 9 3.7 8 29
Processing: 23 37 6.0 37 62
Waiting: 13 23 4.9 24 41
Total: 28 46 7.8 45 82

Percentage of the requests served within a certain time (ms)
50% 45
66% 47
75% 49
80% 50
90% 56
95% 62
98% 68
99% 73
100% 82 (longest request)

So Mediawiki can deal with more than 2,5 times as much requests now.

Some people use Apache’s mod_disk_cache to cache Mediawiki pages, but I prefer Mediawiki’s own caching system because it is more standard and does not require patching Mediawiki, even if it might not get as much benefit as a real proxy or mod_disk_cache.

Improving performance by using tmpfs

Posted on by Frederik

Today I analyzed disk reads and writes on a server with iotop and strace and found some interesting possible optimizations.

With iotop you can check which processes are reading and writing from the disks. I always press the o, p and a keys in iotop so that it only shows me processes doing I/O and so that it will show accumulated I/O instead of the bandwidth. With the left and right arrows I select on which columns to sort the list.

Once you have identified the processes wich are doing much I/O, you can check what they are reading or writing with strace, for example
# strace  -f -p $PID  -e trace=open,read,write

(you can leave out read and/or write if this gives too much noise)

This way I identified some locations where processes do lots of read and write operations on temporary files.

For nagios I placed /var/lib/nagios3/spool and /var/cache/nagios3 on a tmpfs, for Amavis /var/lib/amavis/tmp and for PostgreSQL /var/lib/postgresql/8.4/main/pg_stat_tm.

Other candidates you might want to consider: /tmp, /var/tmp and /var/lib/php5. There are probably many others, depending on which services you use.

Is Unity a better alternative to the GNOME Shell?

Posted on by Frederik

After my disappointment with the current GNOME 3.0 development version with GNOME Shell, I thought it would be interesting to compare it with Ubuntu’s Unity. Ubuntu has just published a new alpha version of what will become Ubuntu 11.04, so I used that for a quick test.

On the positive side:

  • On the dock on the left side there is a button which opens the workspace switcher which gives a nice overview of your virtual desktops and their contents. The workspace switcher is easy to find and it looks awesome: this might be exactly what is needed to make more end users finally get to use virtual desktops.
  • The list of Favourite folders is easily accessible by one of the buttons on the dock, as are all mounted volumes and the Thrash, unlike in GNOME Shell. Ubuntu’s desktop also supports desktop icons.
  • Integration of Banshee in the volume mixer applet is nice: the pop-up in the volume mixer will show the playing song and has some buttons to control playback in Banshee. I do not know whether this integration also works for other audio players though.

The negative:

  • Unity uses uses a development version of Compiz which is very unstable. The first time I booted the Ubuntu live CD, Compiz crashed within one minute. In my next test sessions Compiz crashed again different times. Currently GNOME Shell and Mutter are definitely much more stable than Unity and Compiz.
  • Just like GNOME Shell there is no way to show the date in panel, only the time is displayed.
  • When clicking on the Ubuntu icon in the panel, some kind of empty window pops up. Maybe this ought to be the application launcher, but it is clearly not working.
  • The application launcher can be opened from a button on the dock at the left side of the screen. However that button is rather near the bottom of the dock, above the mounted volumes icons. The Application button should be much more easy to find without having to scan all icons on the dock. Maybe this will get fixed when/if the Ubuntu icon launches the application browser.
  • Applications are not organized in categories. Instead I got a huge table of all applications and preferences tools laid out horizontally and vertically. The Scrollbar in the application browser does not seem to be working so I could not access applications which were out of the view.
  • In the application browser, there is something which looks like a text entry field which permits you to search for an application, but I could not type in it.
  • After using the application browser for a few times, it just shows as an empty window, just like the Ubuntu icon. When this happens, you have no possibility to start applications anymore.
  • When moving the mouse over an icon in the application launcher, a white border is drawn around the icon. The border is always a fixed size: if the application name is too long and wrapped over two lines, the border will cover part of the text.
  • Just like in GNOME Shell, it looks like I cannot add custom applets and application launchers in the panel.
  • The panel is used as a global menu bar for applications but not all applications support it: for example Firefox and LibreOffice do not use it. The menu is only shown when moving the mouse over the panel. If my mouse cursor is in an application itself, there is no trace of the menu, so people might be wondering where it is. I do not know whether this is by design or whether it is simply a bug. Personally I am also not convinced that a global menu is nice: when applications are not maximized, you  need to move your mouse back and forward between the application window and the top of the screen, which is cumbersome.
  • Mounted drives are shown in the dock and on the desktop. This looks a bit superfluous at first sight and especially when having lots of partitions on an external disk and lots of applications opened, the dock might become too small to show all icons.
  • It is still GNOME 2.32. You do not have the nice windowless pop-up dialogs from GTK+3, nor the nice date and time applet from GNOME Shell or the chat integration in the notifications. Users will not benefit from the improvements included in GNOME 3 applications.

While GNOME Shell looked like an unpolished and cumbersome to use product, Unity feels like a completely broken proof of concept. In its current state it is even impossible to do anything useful with it because even launching applications is almost impossible.

It is also questionable how Unity will remain usable in the future after Ubuntu 11.04 Natty is out: will they port it to GTK+ 3? And what will they do about the desktop icons, a feature which is currently still provided by Nautilus 2.32, but not present anymore in 3.0?

Canonical has decided to choose Unity as default for its next Ubuntu version because they thought GNOME Shell was not going into the right direction. However, Unity is currently even a much bigger failure than GNOME Shell. I have the feeling that Canonical’s decision was bad for both GNOME and Ubuntu: now we have two different unfinished, unpolished and in the case of Unity even totally broken desktop shells. I am wondering what would be the current state of GNOME Shell if Canonical had decided to dedicate its resources to GNOME Shell instead of Unity… I am also wondering how users will react to a desktop with Unity by default. Will Ubuntu derivatives with a different default desktop, like Mint, take over Ubuntu as the most popular distribution for desktops? Or will GNOME get into a similar crisis like KDE when 4.0 was out and will many users start moving to other desktops, either temporarily or permanently? Or will they just continue using standard GNOME 2.x until the dust settles? I do not have any answer to these questions, but for sure we are arriving at an important crossroads in the history of GNOME.

For screenshots and more information about Ubuntu 11.04 Natty and Unity, I refer to this Tech Drive-in article.

GNOME 3.0: Making the same mistakes as KDE 4.0?

Posted on by Frederik

Yesterday Fedora held a GNOME 3 test day. In order to facilitate testing, they published a Rawhide live CD containing the latest builds of GNOME 3. This is a great opportunity to test the latest GNOME-shell and other new things without having to upgrade your system to unstable alpha stuff. I tried it out on my laptop with Intel graphics chipset.

After a quick test, I am quite disappointed. Just like KDE 4, GNOME 3 tries to explore some new innovative desktop stuff, but just like KDE 4 in its first versions, it feels extremely unpolished and very unfinished, resulting in a rather cumbersome experience.

On the positive side:

  • The desktop feels pretty fast. Starting up applications, using the search function to find applications and the graphical desktop effects are all pretty smooth.
  • The black GNOME shell interface looks nice with subtle but pleasing effects like drop shadows and transparency.
  • There is a nice Expose effect when clicking on activities, nicely showing you all windows running on your system.
  • I have not tried this myself, but it looks like instant messaging is nicely integrated into the desktop. The user menu in the top panel makes it easy to set your status, and you can chat directly from the notifications on the desktop.
  • Just like chatting is nicely integrated,  the user’s agenda is also nicely integrated on the desktop. Just click on the time and see a list of all your appointments at a glance. It looks much nicer than GNOME 2’s calendar view.
  • The fact that some application dialogs now appear to be popping out of the main window and do not have their own window decoration looks nice and avoids clutter. You can see this in the About dialogs in GTK+ applications.

On the negative side:

  • I have the feeling that a lot of space is wasted in the top bar. By default it contains the Activities menu (which is not really a menu and not really needed, because you can open it by just moving your mouse to the top left of your screen), the time, and a few applets (NetworkManager, Accessibility, Volume control, Battery monitor and a user menu allowing to set some personal preferences and instant messaging status. There does not seem to be a way to add application launchers, or any other custom applets.
  • When an application is launched, the name of the application appears in the panel, together with its icon. However, it is a partial version of the large icon, it looks a bit like it is zoomed in. Because the icon is cropped, it is very hard to recognize and looks rather ugly. I fail to understand why they do not simply show the scaled icon.
  • The application launcher is not handy to use. First you have to move your mouse to the top left of the screen to open Activities, then you have to click on Applications, and then you have to move your mouse to the right of your screen to select an application category and move again back to the center of the screen to launch the requested application. This way, launching an application requires much more mouse movements and clicks than simply navigating in the Applications menu in GNOME 2. Moving the search box and application category list to the left, would already be a huge improvement.
  • The list of applications is shown as a table of application icons, laid out both horizontally and vertically. Having to scan the list in two different directions is cumbersome compared to scanning a vertical application menu like in GNOME 2.
  • When opening the application list, by default it shows all applications in alphabetical order. Even if you want to keep this system, I think it would be much nicer to show them like in SUSE’s GNOME appliation launcher, where all icons are still organized by category and separated by the category headers.
  • Under the icons in the application launcher, the name of the application is shown. Or at least a part of the name: most names are shortened by an ellipsis (…) and this is very ugly. For example Transmission becomes “Transmiss…”, Remote Desktop Viewer becomes “Remote…”. There are also no tooltips showing the full name when hovering your mouse over them. LibreOffice is not included on this live CD, but if they are installed will both LibreOffice Writer and LibreOffice Calc become “Libreoffice…” then? It is clear that not seeing the full names at a glance is terrible for finding applications.
  • There does not seem to be support for desktop icons. The ~/Desktop folder contains some .desktop files, but they are not shown on the desktop. Left or right clicking on the desktop does not do anything. This reminds me of KDE 4.0, which also had broken support for desktop icons which was only fixed completely in later KDE versions when the Folder View widget came out.
  • There is no easy way to open your home directory, a bookmarked directory or a removable drive in a file browser except by opening the application launcher and finding the file manager. No more handy Places menu like in GNOME 2, or desktop icons for your home folder and removable disks.
  • There is no way to move the “dock” to another screen border. Personally I would prefer having it at the bottom side of my screen inside of at the left side, but I could not find a way to change that.
  • I do not like the default GTK+ theme too much. The big white scrollbars and high white tab pages look pretty hard to my eyes, and the grey backgrounded toolbars look a bit weird, especially the sunken View combobox  in Nautilus’ toolbar (it has a white line underneath). The default icon theme also needs an update, because it looks old-fashioned to me. I could not find a way to change the themes. There was no Appearance configuration tool in System Settings.
  • The day of the month and month are not shown by default in the date in the top panel. In the Date and Time Settings I could not find a way to show the complete date.
  • Similar to the above problem, it looks like we will not be able to easily configure what will happen when the laptop lid is closed. I have always preferred GNOME’s nice default settings over KDE’s settings clutter , but now I have the feeling that they are going much too far in GNOME 3.

A lot of my criticism seems pretty fundamental and as th final version of GNOME 3.0 is currently scheduled in 2 months (4th of april), it is sure that many of these issues will not be resolved. Just like KDE 4.0, there is definitely potential here. However in its current state, I consider GNOME 3.0 still as a playground for developers and unsuitable for use except by early adopters. Especially the fact that basic features have been removed (desktop icons) and basic tasks have become harder (launching applications) is really unforgivable.

Another interesting read is this quick screenshot based review by a QT developer. Also check out GNOME 3’s official website.

Update: GNOME 3 developer hadess responded to some frequently reported problems during the test day. Some of the problems I have written about here, are currently being worked on.

Server migration to Debian

Posted on by Frederik

Since this afternoon, this server is now running Debian GNU/Linux Squeeze. Just like the previous system, this is a KVM virtual machine running on a HP Proliant DL185G5 host. The host server has always been running Debian. This was my last production system still running Mandriva. I might have forgotten to move over a few things or there might be some breakage somewhere, so let me know if you encounter a problem.

Mandriva’s future? Mageia.

Posted on by Frederik

In spite of the fact that Mandriva has decided on its shareholder’s meeting to publish new release 2011 at the end of the first half of 2011 and to improve its communication towards the community, one can safely say that both the distribution and the company do not have any realistic future anymore. A bunch of ex-employees (most of them fired when Edge-IT was liquidated) and a big part of the community, have decided to fork the distribution under the new name Mageia. Now with only a handful of developers left and with most of the community contributors moved to Mageia, I do not see how new Mandriva releases will happen anymore in the future. Let’s hope that the Mageia community manages to take over what is left from Mandriva and that it can become a nice distribution bringing Linux to the masses.