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тАО02-07-2010 03:42 AM
тАО02-07-2010 03:42 AM
NFS asynchronous Vs. synchronous writes
We want to implement an archive solution for the databases (2 servers) and the application servers (2 servers), all of them are HP-UX 11.23, Itanium servers. We will mount a NFS exported share from NAS storage. my concerns revolve around what best mode to use (if NAS supported it) asynchronous or synchronous?
As far as I know, synchronous is the default and its preferred because of the data integrity, also as what is written here about "Safe Asynchronous Writes":
http://forums11.itrc.hp.com/service/forums/questionanswer.do?admit=109447626+1265529583347+28353475&threadId=1139502
it seems that the asynchronous mode on NFS V.3 resolved the data corruption problems in case the NFS server goes down while the clients are writing to it.
The other concern is to use boid or not? if yes, is there any recommended number other than the default one?
I'm planning to start with the default value, then trying to increase and decrease the value while monitoring to achieve the best value?
Note: Its an archiving solution, and its about 3TB space, the DB's going to use it once a week but I'm pretty sure they will use it heavily.
BR
Mohammad
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тАО02-07-2010 06:31 AM
тАО02-07-2010 06:31 AM
Re: NFS asynchronous Vs. synchronous writes
Since it's an archiving solution, why do you care if the server goes down? Just as long as you can back up your database before that happens or be able to restart.
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тАО02-07-2010 11:02 PM
тАО02-07-2010 11:02 PM
Re: NFS asynchronous Vs. synchronous writes
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тАО02-07-2010 11:52 PM
тАО02-07-2010 11:52 PM
Re: NFS asynchronous Vs. synchronous writes
Speed may be more important.
And depending on how you are copying the data, if the server goes down, you may not have a restart capability anyway.
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тАО02-08-2010 12:07 AM
тАО02-08-2010 12:07 AM
Re: NFS asynchronous Vs. synchronous writes
asynchronous read-ahead and write-behind requests.
So biod would run with async and I suppose this would be the better way in your case.
Regarding number of biod i think below link would give you some idea
http://publib.boulder.ibm.com/infocenter/pseries/v5r3/index.jsp?topic=/com.ibm.aix.prftungd/doc/prftungd/num_necessary_biod_threads.htm
BR,
Kapil+
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тАО02-08-2010 10:05 AM
тАО02-08-2010 10:05 AM
Re: NFS asynchronous Vs. synchronous writes
The number of nfsds one "needs" depends on how many concurrent NFS requests you need the server to service.
The number of biods on any given client will depend on how many concurrent NFS requests it needs/wants to have outstanding to the server at one time.
Those will all depend on things like the link bandwidth between the client(s) and the server, and the latency.
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тАО02-08-2010 10:55 AM
тАО02-08-2010 10:55 AM
Re: NFS asynchronous Vs. synchronous writes
You pay your money you take your choice.
asynchronous writes get you better performance. But if there is a sudden stop on your system you are much more likely to lose written data.
No OS upgrade or new version of NFS can eliminate the risk of data loss.
That risk increases with how busy your system is.
The good news is Oracle is well written and can recover you almost to the last transaction even with a sudden loss of power with no backup.
SEP
Owner of ISN Corporation
http://isnamerica.com
http://hpuxconsulting.com
Sponsor: http://hpux.ws
Twitter: http://twitter.com/hpuxlinux
Founder http://newdatacloud.com
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тАО02-08-2010 11:14 AM
тАО02-08-2010 11:14 AM
Re: NFS asynchronous Vs. synchronous writes
I currently have 24 NFS file systems with async writes mounted from 3 servers. When one of the master's go down then the 3 masters have to be reexported and 24 clients have to be remounted. It takes a minute or two with a script and it is perform as often as once a month. During patching for example.
I have never heard of any loss of data complaints from any SAP or oracle admins or DBA's, nor any complaints from the users.
The key is to re-export first and then remount. And like I said above, it only takes a minute or two with a script.
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тАО02-08-2010 12:29 PM
тАО02-08-2010 12:29 PM
Re: NFS asynchronous Vs. synchronous writes
The default value of 16 biods is a good starting point. I would start there and monitor performance.
I'd also recommend tuning the 11.23 systems using the tuning guidelines in Appendix A of the KRPC guide found here:
http://docs.hp.com/en/14765/v2963139.pdf
Tunable Default Recommended
nfs_async_read_avoidance_enabled 0 1
nfs_fine_grain_fs_lock 0 2
nfs_new_lock_code 0 1
nfs_new_rnode_lock_code 0 1
nfs_wakeup_one 0 2
nfs3_new_acache 0 1
Note: I am not recommending tuning the nfs_exportfs_rwlock parameter as there has been a recent report of problems involving this tunable on NFS servers.
Regards,
Dave
[Any personal opinions expressed are mine, and not official statements on behalf of Hewlett Packard Enterprise]
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тАО02-09-2010 11:22 PM
тАО02-09-2010 11:22 PM
Re: NFS asynchronous Vs. synchronous writes
I tested the the NAS share with the basic timex and dd commands as the following:
I issued the command:
timex dd if=/dev/zero of=/myshare/test bs=1024k count=10240
First time, I kept biod number on the default (16), it gave me 2m 57 seconds
Second time, I increased the biod number to 32, it gave me 2m 23s.
Third time, I increased the biod number to 63, it gave me 2m 55s.
Fourth time, I made biod=0, it gave me 5m 22s.
So, I decided to go with the second configuration. For now, am still monitoring to see if I can enhance the throughput.
I'll update you if there is any new news.
BR
Mohammad