Ext4 sysfs parameters

Have you ever wondered how much data written to your Ext4 filesystem since it's first creation time or last mount time. Here is two ext4 sysfs parameters that will tell you the magic numbers you need.

/sys/fs/ext4//lifetime_write_kbytes

/sys/fs/ext4//session_write_kbytes

Here is some more ext4 sysfs paramters and their meanings, but mostly tuning of ext4 multiblock allocator. ext4 sysfs paramters

Freebsd ciss driver logical drive limit

Lately, I was faced with a strange problem on a HP server which uses HP Smart Array controller P800 which is running Freebsd. All my 24 hard drives which is hosted on externel HP enclosures was presented as 24 single raid0 logical volumes. Surprisingly, when the freebsd booted it doesn't presented the disks and disabled the ciss driver (HP Smart Array Controller) with following message

Mar 12 16:00:41 freebsd kernel: ciss1: adapter claims to report absurd
number of logical drives (24 > 15)

A quick check on the driver source code showed up that there is a hard limit defined to 15.(/usr/src/sys/dev/ciss/cissvar.h)

 #define CISS_MAX_LOGICAL        15

So I wanted to be sure if I change the number to a higher value , won't do any unwanted behavior later on the system. In that point I contacted Paul Saab where he explained the limit as  below.

 really that's done to limit the amount of memory needed upfront by the
driver.  I believe you can easily increase the number of drives
without issue as long as you have enough memory below 4GB.  Parts of
the ciss driver require that the memory you DMA from be under 4G

After the clarification, I just set the number to 32 and rebuild/install the kernel, restart the machine and a quick check on dmesg showed up all my 24 logical volumes presented on HP P800 controller.

Mar 13 10:32:37 freebsd kernel: da19: 286070MB (585871964 512 byte sectors: 255H 32S/T 65535C)
Mar 13 10:32:37 freebsd kernel: da20 at ciss1 bus 0 scbus2 target 19 lun 0 
Mar 13 10:32:37 freebsd kernel: da20:  Fixed Direct Access SCSI-5 device
Mar 13 10:32:37 freebsd kernel: da20: 135.168MB/s transfers
Mar 13 10:32:37 freebsd kernel: da20: Command Queueing enabled
Mar 13 10:32:37 freebsd kernel: da20: 286070MB (585871964 512 byte sectors: 255H 32S/T 65535C)
Mar 13 10:32:37 freebsd kernel: da21 at ciss1 bus 0 scbus2 target 20 lun 0 
Mar 13 10:32:37 freebsd kernel: da21:  Fixed Direct Access SCSI-5 device
Mar 13 10:32:37 freebsd kernel: da21: 135.168MB/s transfers
Mar 13 10:32:37 freebsd kernel: da21: Command Queueing enabled
Mar 13 10:32:37 freebsd kernel: da21: 286070MB (585871964 512 byte sectors: 255H 32S/T 65535C)
Mar 13 10:32:37 freebsd kernel: da22 at ciss1 bus 0 scbus2 target 21 lun 0 
Mar 13 10:32:37 freebsd kernel: da22:  Fixed Direct Access SCSI-5 device
Mar 13 10:32:37 freebsd kernel: da22: 135.168MB/s transfers
Mar 13 10:32:37 freebsd kernel: da22: Command Queueing enabled
Mar 13 10:32:37 freebsd kernel: da22: 286070MB (585871964 512 byte sectors: 255H 32S/T 65535C)
Mar 13 10:32:37 freebsd kernel: da23 at ciss1 bus 0 scbus2 target 22 lun 0 
Mar 13 10:32:37 freebsd kernel: da23:  Fixed Direct Access SCSI-5 device
Mar 13 10:32:37 freebsd kernel: da23: 135.168MB/s transfers
Mar 13 10:32:37 freebsd kernel: da23: Command Queueing enabled
Mar 13 10:32:37 freebsd kernel: da23: 286070MB (585871964 512 byte sectors: 255H 32S/T 65535C)
Mar 13 10:32:37 freebsd kernel: da24 at ciss1 bus 0 scbus2 target 23 lun 0 
Mar 13 10:32:37 freebsd kernel: da24:  Fixed Direct Access SCSI-5 device
Mar 13 10:32:37 freebsd kernel: da24: 135.168MB/s transfers
Mar 13 10:32:37 freebsd kernel: da24: Command Queueing enabled
Mar 13 10:32:37 freebsd kernel: da24: 286070MB (585871964 512 byte sectors: 255H 32S/T 65535C)

Linux like dmesg in Freebsd

UPDATE:  this patch is applied to Freebsd repository on  10 May 2013

http://svnweb.freebsd.org/base?view=revision&revision=250430

In my previous post, I was talking about the "dmesg -c" equivalent in FreeBSD. Simply it was a sysctl command. So, I decided to simply change FreeBSD dmesg command and make it act like in as Linux. All you have to do is download my patch and apply it as shown below.I was tested the patch on FreeBSD 9 btw.

mybsd# pwd
/usr/src/sbin/dmesg
mybsd# patch < dmesg.patch 
Hmm...  Looks like a unified diff to me...
The text leading up to this was:
--------------------------
|--- dmesg.c.org        2012-01-03 19:04:44.000000000 +0200
|+++ dmesg.c    2012-02-28 11:36:22.000000000 +0200
--------------------------
Patching file dmesg.c using Plan A...
Hunk #1 succeeded at 81.
Hunk #2 succeeded at 194.
Hunk #3 succeeded at 204.
done
mybsd# make 
Warning: Object directory not changed from original /usr/src/sbin/dmesg
cc -O2 -pipe  -std=gnu99 -fstack-protector -Wsystem-headers -Werror -Wall -Wno-format-y2k -W -Wno-unused-parameter -Wstrict-prototypes -Wmissing-prototypes -Wpointer-arith -Wreturn-type -Wcast-qual -Wwrite-strings -Wswitch -Wshadow -Wunused-parameter -Wcast-align -Wchar-subscripts -Winline -Wnested-externs -Wredundant-decls -Wold-style-definition -Wno-pointer-sign -c dmesg.c
cc -O2 -pipe  -std=gnu99 -fstack-protector -Wsystem-headers -Werror -Wall -Wno-format-y2k -W -Wno-unused-parameter -Wstrict-prototypes -Wmissing-prototypes -Wpointer-arith -Wreturn-type -Wcast-qual -Wwrite-strings -Wswitch -Wshadow -Wunused-parameter -Wcast-align -Wchar-subscripts -Winline -Wnested-externs -Wredundant-decls -Wold-style-definition -Wno-pointer-sign  -o dmesg dmesg.o -lkvm

Clearing FreeBSD Kernel Message Buffer

As you can clear kernel message buffer on Linux with dmesg command " dmesg -c ", it's a little bit different on a BSD system.It's done by sysctl as following

# sysctl kern.msgbuf_clear=1