[Asterisk-Users] Hard drive write cache

Tue Jun 13 12:36:44 MST 2006

Thanks for the suggestions.

CF is not an option for FreePBX which is a requirement for the installs I
have in mind.  Astlinux on CF is a great option otherwise.  That is by far
the simplest, cheapest, and suprisingly most reliable solution I have come
across so far.  If there was a half decent (open source) GUI that could run
on Astlinux on CF it would be a no brainer IMHO.

Physically locking down the server is not an option.  It will be hung on the
wall in place of where a traditional PBX would normally go.  This is a
telecom closet NOT a server rack environment.  UPS with auto shut down is
just one link in the chain.  Do you have any further information of locking
plugs?  I have not come across those before.  Of course in order for that to
make sense I would need locking plugs on both the server AND UPS end.  It
has to be idiot proof.

Think PBX and/or network appliance not computer server.  They are idiot
proof so it is quite reasonable IMHO to expect the same from an Asterisk
server (or in my way of thinking, Asterisk network appliance).

> -----Original Message-----
> From: Nicholas Kathmann 
> [mailto:nicholas.kathmann at kathmannconsulting.com] 
> Sent: Tuesday, June 13, 2006 11:04 AM
> To: Asterisk Users Mailing List - Non-Commercial Discussion
> Subject: Re: [Asterisk-Users] Hard drive write cache
> 
> If all you are worried about is the write cache on the disks, 
> why not just put the system on a UPS set to shutdown the 
> system in the event of power failure, then place both the UPS 
> and asterisk servers in a locked rack.  In the event of a 
> power failure (or someone knocking the plug loose, which you 
> can use locking plugs to further mitigate), the system will 
> stay up on battery power then shut itself down to prevent 
> data corruption.  I doubt you will get that level of uptime, 
> but there are other options to help achieve higher 
> reliability.  You can run the OS and asterisk on a solid 
> state disk, and have voicemail and whatever else you want to 
> go to rotating disks.  That will also help with power usage 
> on the server when using the UPS.  Industrial flash disks are 
> said to have (but they really can't promise this) a 3 million 
> hour MTBF.
> 
> Thanks,
> Nick
> 
> shadowym wrote:
> > 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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> 