xfs
[Top] [All Lists]

Re: XFS and net devices, any pros or cons ?

To: linux-xfs@xxxxxxxxxxx
Subject: Re: XFS and net devices, any pros or cons ?
From: "Blizbor (IMA)" <tb670725@xxxxxx>
Date: Fri, 16 Aug 2002 12:23:43 +0200
References: <20020814171123.FZMF1197.imf05bis.bellsouth.net@TAZ2> <1029345349.15708.98.camel@jen.americas.sgi.com>
Sender: owner-linux-xfs@xxxxxxxxxxx
User-agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.0.0) Gecko/20020530
Steve Lord wrote:
On Wed, 2002-08-14 at 12:08, Greg Freemyer wrote:

>>  The normal way we setup something like this is to use a shared scsi
>>  or fiberchannel disk setup, that way you no longer have a singe
>>  point of failure. If you are putting the disks into one of the
>>  two computers then if that system goes down you are dead in the
>>  water. The other aspect of the above setup is using something
>>  like failsafe, the two nodes monitor each other, and can (if
>>  setup correctly) shoot the other node down and take over the
>>  filesystem if it detects problems. failsafe itself is opensource,
>>  not sure if the components of it which fail over the filesystem
>>  to the other node are. Of course all this assumes using the fs
>>  via NFS - the second node takes over the ip address of the failed
>>  node.

>>  A quick look at drbd on the net seems to show that it is designed
>>  for these sorts of setups, and it has links to all the high
>>  availability stuff for linux.

>> That aside, there should be no problem doing this, provided you
>> make sure the unmount from one system is complete before attempting
>> to mount on the other system. Mounting a filesystem which is >> already mounted elsewhere is not a good thing, the second system
>> will think the fs needs recovery running on it.


>>  Steve

I don't think drbd is designed for use in a shared SCSI environment.


I did not intend to imply it was, just presenting a different way
to build a resilient configuration.


This what I'm building isn't shared SCSI. I'm believe that shared SCSI couldn't survive some kind of crashes. I prefer two complete, independent machines which are mirroring some storage via LAN and replicate some data using native protocols of some services.


It is more of a RAID 1 driver where the 2 halves of the mirror are on the 2 different servers using internal disks.

I believe it has support for ordered writes, but I for one would not simply 
assume XFS and drbd are compatible.



Ah, I should have read more.... if the fs is mirrored between the two
hosts then there is a chance it will work OK. However, the interesting
part of XFS is write ordering - there are certain writes which we need
to know have made it down to disk and will survive a crash. In this
sort of setup I really do not know where the data will be once drbd
says it is written. Probably still in cache on the remote box for a
start. There may well be circumstances where loss of both machines
will cause filesystem corruption.

you are right, testing such a setup before going live with it is
important, please do not take my comments as meaning it will definitely
work.

Steve,

there are few modes of operation of the drbd:
a) - send and forgot
b) - send and OK is when recive acknowledge is returned
c) - send and OK is when write on remote is commited

So, what exactly data should be synced ?

I'm thinking, that during creation of XFS filesystem
on lets say /dev/sdb1 (16GB) i will create logs on
/dev/sdb2 (128MB or 256MB or less - must calculate exact size)

Then: /dev/sdb1 (data) will be mirrored using mode b,
and /dev/sdb2 (logs) will mirror using mode c.
Nothing will use mode a.

Is it wright ?

Regards,
Blizbor


<Prev in Thread] Current Thread [Next in Thread>