[Asterisk-Users] Hard drive write cache

[shadowym]

The cold hard truth is that if Asterisk cannot achieve 99.999% uptime
without becoming much more expensive that a traditional PBX then it is not a
viable alternative.  Even elcheapo Key systems are rated for five nines.
That is what the telco world requires unless your just using Asterisk in
your basement as a hobby or as a one man company.

Redundant Servers is moving into the realm of non-competitive with
Traditional PBX IMHO.

I don't care about corruption of the CDR or any of the logging/database
information.  All I care about is the ability make phone calls after power
failure.  That IS the MAIN function of a PBX.  Not call centers, databases,
CDR, click 2 call, and all the other bells and whistles.

 

> -----Original Message-----
> From: Boris Bakchiev [mailto:boris at jildent.com.au] 
> Sent: Tuesday, June 13, 2006 2:13 AM
> To: Asterisk Users Mailing List - Non-Commercial Discussion
> Subject: RE: [Asterisk-Users] Hard drive write cache
> 
> These days you don't have to worry much about your write 
> cache unless you're running application where once single 
> byte changed will affect whole file.
> 
> Look at it this way, the only corruption will occur is 
> whatever the files were open by asterisk at the time of the 
> crash. And only up to the point where the file was last open. 
> As far as I know asterisk does not keep cdr or log files open 
> so you would loose only the data that was written at the time 
> of the power failure.
> 
> Any journaling file system (ext3, resierfs, xfs, etc) will 
> easily handle any power failure event. Your files will not be 
> corrupt but could miss some of the data.
> 
> At the most you will loose 10-50 cdr entries written to you log files.
> 
> If you post CDR to a remote SQL database then you asterisk 
> install and linux is more or less static and will not be 
> affected by the power failure.
> 
> What you need to do is minimise the writes to hard disk's:
> 
> 1 - Send syslog to remote server and do not do ANY syslogs
>     Or keep the circular buffer in memory if you have plenty of it. 
> 2 - Send CDR's to SQL server (or log to ramdisk and send to 
> remote server every few minutes via SSH)
> 3 - Do not record any calls (or do that somewhere else)
> 4 - Stop any services that write/read data on regular intervals.
> 
> If you have no writes you have nothing to worry about during 
> power failure and journaling file system will take care of the rest.
> 
> Keep your partition size really small so that fsck will not 
> take much time.
> 
> You have to be realistic, you cannot achieve 99.999% uptime. 
> That's 5 minutes per year downtime.
> You will have more or less 100% until your first hardware failure.
> 
> Even if you have all the hardware components pre-purchased it 
> will still take you 2-12 hours to detect, diagnose and fix 
> the fault if you lucky.
> So your 5 minuets 
> 
> If the business is demanding 99.999% then it should be 
> prepared to invest into the hardware.
> I would recommend a cluster or even better a fault tolerant server.
> Those are expensive but you can pretty much rule out the 
> hardware failure and swap all of the failed components while 
> the system is running (cpu, memory, hdd, etc).
> 
> Look at Stratus or NEC FT servers if you need hardware redundancy.
> They're expensive but will give you the hardware reliability you need.
> 
> Or get a traditional PABX :)
> 
> 
> 
> > -----Original Message-----
> > From: asterisk-users-bounces at lists.digium.com 
> [mailto:asterisk-users- 
> > bounces at lists.digium.com] On Behalf Of shadowym
> > Sent: Tuesday, 13 June 2006 10:34
> > To: asterisk-users at lists.digium.com
> > Subject: [Asterisk-Users] Hard drive write cache
> > 
> > 
> > I am looking at ways to harden my asterisk install to 
> prevent computer 
> > related issues from happening.  I am concerned about about 
> disk write 
> > cache.
> > That seems to be a major source of hard drive corruption on power
> failure.
> > Hard Drive corruption is simply unacceptable for the 99.999% uptime 
> > requirements of my Asterisk install that needs to be as 
> reliable as a 
> > proprietary PBX.
> > 
> > Of course I will be using redundant power supplies, raid 1 and use a
> UPS.
> > None of those things mean much if the power cords accidentally get
> pulled
> > from the back of the server.  Unlikely as it may be I have 
> to consider
> ALL
> > possibilities.
> > 
> > So is disabling the write cache a good way to reduce the 
> risk of hard 
> > drive corruption for an Asterisk server?  I am not too 
> concerned about 
> > the reduced performance/lifetime of hardrives with write cache 
> > disabled since
> Asterisk
> > is not a very write intensive environment.  Even with lot's of
> voicemail
> > going on.
> > 
> > Any other recommendations/links for increasing the reliability of
> Asterisk
> > servers?
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