How can I permanently turn off 'Write Cache' ---Debian

rickh · 03-12-2006, 01:05 PM

I have been working on setting up some POSTGRESQL databases ... Nothing critical yet, but I'm getting ready. Did a dist-upgrade this morning, and POSTGRESQL was one of the programs updated. When it restarted, there was a message:

Quote:

Starting PostgreSQL 7.4 database server: main.
Warning: The following devices contain databases and have write
caching enabled: /dev/hdb
This could destroy the integrity of your databases in the event of power
failure. Consider disabling the write cache with "hdparm -W 0 <device>".

The hdparm command does the job, but after a reboot, 'write caching' is enabled again.

What is the correct way to turn it off permanently?

Keruskerfuerst · 03-13-2006, 07:31 AM

Write cache is enabled by default in the kernel.
Add a bootscript with the following lines to runlevel 5:
#!/bin/bash
hdparm -W0 /dev/hdb

rickh · 03-13-2006, 10:25 AM

Quote:

Add a bootscript ... to runlevel 5:

I am aware that such a thing can be done, but vague about just how to go about it. As far as I can tell there are currently no 'bootscripts' on my system apart from the various bashrc files. Just where would this script go, and what would initialize it?

rickh · 03-13-2006, 06:56 PM

I have searched around a whole lot more for instructions on how to do this ... unsuccessfully. I guess what I really want to know is if there is a 'Debian' way. Even better, is there a system script already out there in which I should just append the line 'hdparm -W0 /dev/hdb'

J.W. · 03-13-2006, 08:03 PM

Moved to Distributions - Debian per request

kushalkoolwal · 03-13-2006, 08:24 PM

Quote:

Originally Posted by rickh

I am aware that such a thing can be done, but vague about just how to go about it. As far as I can tell there are currently no 'bootscripts' on my system apart from the various bashrc files. Just where would this script go, and what would initialize it?

You can put the hdaprm command in /etc/hdparm.conf file towards the end. So Everytime you reboot your system, it will execute the command and you will be able to disable the write cache.

rickh · 03-13-2006, 08:35 PM

Ah! That's exactly what I needed. If fact, such a line is already there, I just have to uncomment it. Thanks.

kushalkoolwal · 03-13-2006, 09:10 PM

Quote:

Originally Posted by rickh

Ah! That's exactly what I needed. If fact, such a line is already there, I just have to uncomment it. Thanks.

No problems...

rickh · 03-13-2006, 09:21 PM

...Except, it didn't work. I tried a couple optional methods described in /etc/hdparm.conf:

Code:

/dev/hdb {
       write_cache = off
}

and

Code:

command_line {
        hdparm -W0 /dev/hdb
}

but either way after a reboot:

Quote:

debian:~# hdparm -i /dev/hdb

/dev/hdb:

Model=WDC WD800JB-00JJC0, FwRev=05.01C05, SerialNo=WD-WMAM98691672
Config={ HardSect NotMFM HdSw>15uSec SpinMotCtl Fixed DTR>5Mbs FmtGapReq }
RawCHS=16383/16/63, TrkSize=0, SectSize=0, ECCbytes=66
BuffType=unknown, BuffSize=8192kB, MaxMultSect=16, MultSect=off
CurCHS=16383/16/63, CurSects=16514064, LBA=yes, LBAsects=156301488
IORDY=on/off, tPIO={min:120,w/IORDY:120}, tDMA={min:120,rec:120}
PIO modes: pio0 pio3 pio4
DMA modes: mdma0 mdma1 mdma2
UDMA modes: udma0 udma1 udma2 udma3 udma4 *udma5
AdvancedPM=no WriteCache=enabled
Drive conforms to: Unspecified: ATA/ATAPI-1 ATA/ATAPI-2 ATA/ATAPI-3 ATA/ATAPI-4 ATA/ATAPI-5 ATA/ATAPI-6

* signifies the current active mode

Evidently that script is not being invoked during the boot?

kushalkoolwal · 03-13-2006, 09:30 PM

Quote:

Originally Posted by rickh

...Except, it didn't work. I tried a couple optional methods described in /etc/hdparm.conf:

Code:

/dev/hdb {
       write_cache = off
}

and

Code:

command_line {
        hdparm -W0 /dev/hdb
}

but either way after a reboot:
Evidently that script is not being invoked during the boot?

Well sad to know that. Actually on my system, the script gets invoked everytime I boot my system.

Ah, I just observed that I have script called hdparm in my /etc/init.d directory which is linked to rcN.d directories and that's why it is getting invoked in my case. It was there by default.

Is there any script in your system ??

rickh · 03-13-2006, 10:01 PM

Yeah. I have such a script, and also I notice that /etc/rcS.d/ includes S07hdparm

Is that where it belongs?