[Cluster-devel] GFS + iscsi target + LVM performance and file integrity

[Cluster-devel] GFS + iscsi target + LVM performance and file integrity

[अनुज Anuj Singh]

Hi,
I have a question related to GFS + LVM and iscsi.
1). I have a file test.txt on shared GFS file system, some user ramesh opens
test.txt to read, at the same time some other user Smith on the network
writes some data to test.txt file.
What data will Ramesh see in test.txt file which is changed after he opened?

How does GFS handles data integrity?

2). The other question I have related to the performance issue using LVM.
Say I have iscsi-target nodes TargetNode1 TargetNode2
TargetNode3.......TargetNode N and I created a LVM on my SAN head
(issi-initiator) using /dev/sda, /dev/sdb, /dev/sdc/ ......./dev/sdaN ( raw
disks from my iscsi-target machines)
What will be impact of adding more storage (iscsi-targets) over file lookup
performance? I am using nfs to export the file system. The data supposed to
be around 8TB to 12 TB.

Thanks and Regards
Anuj Singh.
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[Cluster-devel] GFS + iscsi target + LVM performance and file integrity

[Christine Caulfield]

???? Anuj Singh wrote:
> Hi,
> I have a question related to GFS + LVM and iscsi.
> 1). I have a file test.txt on shared GFS file system, some user ramesh
> opens test.txt to read, at the same time some other user Smith on the
> network writes some data to test.txt file.
> What data will Ramesh see in test.txt file which is changed after he
> opened?
> How does GFS handles data integrity?

The same thing happens on GFS as would occur if you did that on a local
file system. GFS does not provide any additional data integrity features
over other file systems. If you can corrupt a file by writing to it from
two places using ext3 on one node, then the same thing will happen using
GFS, regardless of whether the processes are on the same or different nodes.

The point of GFS is not to provide data integrity, but /metadata/
integerity. ie, the filesystem itself does not become corrupted by two
nodes writing to the same inode or directory.

So, the basic rule is: if it would corrupt data if two people on the
same node did it on next3, then it will also corrupt data if two people
on different nodes did it on GFS.

I hope that's clear!
-- 

Chrissie

[Cluster-devel] GFS + iscsi target + LVM performance and file integrity

[अनुज Anuj Singh]

Hi,
Thanks for the reply.
I found this page, talking about simultaneous read/write to a single file
system.

http://www.redhat.com/gfs/
snap--------------------
Red Hat GFS is commonly used in clusters of enterprise applications to
provide high speed access to a consistent file system image across the
server nodes. This allows the cluster nodes to simultaneously read and write
to a single shared filesystem. Typical application clusters where Red Hat
GFS is deployed today include:
-------------------------end of snap


Please can I have some technical idea, doc or flow chart type of thing
regarding GFS mechanism.
Thanks and Regards
Anuj Singh.

On Wed, Apr 30, 2008 at 1:00 PM, Christine Caulfield <ccaulfie@redhat.com>
wrote:

> ???? Anuj Singh wrote:
> > Hi,
> > I have a question related to GFS + LVM and iscsi.
> > 1). I have a file test.txt on shared GFS file system, some user ramesh
> > opens test.txt to read, at the same time some other user Smith on the
> > network writes some data to test.txt file.
> > What data will Ramesh see in test.txt file which is changed after he
> > opened?
> > How does GFS handles data integrity?
>
> The same thing happens on GFS as would occur if you did that on a local
> file system. GFS does not provide any additional data integrity features
> over other file systems. If you can corrupt a file by writing to it from
> two places using ext3 on one node, then the same thing will happen using
> GFS, regardless of whether the processes are on the same or different
> nodes.
>
> The point of GFS is not to provide data integrity, but /metadata/
> integerity. ie, the filesystem itself does not become corrupted by two
> nodes writing to the same inode or directory.
>
> So, the basic rule is: if it would corrupt data if two people on the
> same node did it on next3, then it will also corrupt data if two people
> on different nodes did it on GFS.
>
> I hope that's clear!
> --
>
> Chrissie
>
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[Cluster-devel] GFS + iscsi target + LVM performance and file integrity

[अनुज Anuj Singh]

Sorry I got that, it's the file system integrity rather than "file/data"
integrity.
Thanks.

The other thing on my mind is:
What would be the impact of adding more iscsi-target nodes to my LVM/GFS
over SAN head?
Does it going to make an impact over file seek time (file lookup read/write)
for the client machine accessing a file over GFS?
f.e. a file's data can be stored on iscsi-target nodeA , some data on
iscsi-target nodeX.

More disk space == more file lookup time?

in case such thing does not happens then why? How does it works?

Thanks and regards
Anuj Singh


On Wed, Apr 30, 2008 at 2:37 PM, ???? Anuj Singh <anujhere@gmail.com> wrote:

> Hi,
> Thanks for the reply.
> I found this page, talking about simultaneous read/write to a single file
> system.
>
> http://www.redhat.com/gfs/
> snap--------------------
> Red Hat GFS is commonly used in clusters of enterprise applications to
> provide high speed access to a consistent file system image across the
> server nodes. This allows the cluster nodes to simultaneously read and write
> to a single shared filesystem. Typical application clusters where Red Hat
> GFS is deployed today include:
> -------------------------end of snap
>
>
> Please can I have some technical idea, doc or flow chart type of thing
> regarding GFS mechanism.
> Thanks and Regards
> Anuj Singh.
>
> On Wed, Apr 30, 2008 at 1:00 PM, Christine Caulfield <ccaulfie@redhat.com>
> wrote:
>
> > ???? Anuj Singh wrote:
> > > Hi,
> > > I have a question related to GFS + LVM and iscsi.
> > > 1). I have a file test.txt on shared GFS file system, some user ramesh
> > > opens test.txt to read, at the same time some other user Smith on the
> > > network writes some data to test.txt file.
> > > What data will Ramesh see in test.txt file which is changed after he
> > > opened?
> > > How does GFS handles data integrity?
> >
> > The same thing happens on GFS as would occur if you did that on a local
> > file system. GFS does not provide any additional data integrity features
> > over other file systems. If you can corrupt a file by writing to it from
> > two places using ext3 on one node, then the same thing will happen using
> > GFS, regardless of whether the processes are on the same or different
> > nodes.
> >
> > The point of GFS is not to provide data integrity, but /metadata/
> > integerity. ie, the filesystem itself does not become corrupted by two
> > nodes writing to the same inode or directory.
> >
> > So, the basic rule is: if it would corrupt data if two people on the
> > same node did it on next3, then it will also corrupt data if two people
> > on different nodes did it on GFS.
> >
> > I hope that's clear!
> > --
> >
> > Chrissie
> >
>
>
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