Subject: MBX mailboxes over iSCSI

From: Yiorgos Adamopoulos <[email-masked]>
Date: Tue, 23 Nov 2004 13:39:09 +0200

Does anybody have any experiense on such a configuration?  iSCSI 
partitions look like local disks to the OS (or at least this is my 
understandig) but in truth they reside on another server on the network.

I am going to have 20K mailboxes, but by 2005/06 I may be forced to 
increase this number to an order of magnitude (nearing 100K)
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From: Mark Crispin <[email-masked]>
Date: Tue, 23 Nov 2004 08:56:35 -0800 (PST)

On Tue, 23 Nov 2004, Yiorgos Adamopoulos wrote:
> Does anybody have any experiense on such a configuration?  iSCSI partitions 
> look like local disks to the OS (or at least this is my understandig) but in 
> truth they reside on another server on the network.

I doubt very much that mbx format will work on any network filesystem, 
even if the locking problem is solved.  The only network filesystem that I 
know of in which mbx would work was the old TOPS-20 from two decades ago, 
and only because that filesystem had rigorous token passing on a page to 
guarantee that updates were atomic across all users of the network 
filesystem.

-- Mark --

http://staff.washington.edu/mrc
Science does not emerge from voting, party politics, or public debate.
Si vis pacem, para bellum.

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From: Guy Dawson <[email-masked]>
Date: Tue, 23 Nov 2004 18:07:40 +0000

Mark Crispin wrote:
> even if the locking problem is solved.  The only network filesystem that 
> I know of in which mbx would work was the old TOPS-20 from two decades 
> ago, and only because that filesystem had rigorous token passing on a 
> page to guarantee that updates were atomic across all users of the 
> network filesystem.

It's my understanding that iSCSI does not implement a network filesystem
but simply (?) a way to transport a SCSI bus over an IP infrastructure.

iSCSI servers can be configured to support multiple seperate iSCSI
targets (logical disks) for multiple seperate iSCSI clients (servers).
Each server having it's own logical disk. In this instance there is no
shared file system. However all file systems are stored on a single
storage server which can then have a central backup system.

Chances are an iSCSI server can be configured to enable to clients to
access the same filesystem. At this point if the two clients cannot
co-ordinate access then IMAP won't be able to either.

Guy
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[email-masked]         07973  797819                01753 776104

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From: Mark Crispin <[email-masked]>
Date: Tue, 23 Nov 2004 10:48:18 -0800 (Pacific Standard Time)

> storage server which can then have a central backup system.

If that is the case, it *may* work if locking is solved.

The instant that there is more than one client that has access to one of 
those filesystems, it will not work.

-- Mark --

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From: Richard Westlake <[email-masked]>
Date: Tue, 23 Nov 2004 19:00:38 +0000 (GMT Standard Time)

Hi all

I would also be interested in hearing about anyone using SAN technologies
especially iSCSI to provide storage to a sendmail/IMAP server?

I like to idea of being able to move the storage off the server to improve
reliability.
We could move the service (and data) between servers with just a few
commands, useful when a server fails. Software updates could be installed
and tested during the week on a backup server with only a small brake in
service when they are put into production, should reduce the amount of
weekend and out of hours working.

>From comments on the list I/O  seems to be critical performance factor, I
don't know if iSCSI would cause problems with this.

My setup is probably quite small, with several hundred user but less than
100 actually connected at anyone time and the total disk space for email
is about 45Gbyte.

We have a small number of users who don't use folders and keep everything
in their inbox. As a result some of the inboxes contain thousands of
messages and range in size from a few hundred Mbyte to over a Gbyte,
opening these takes some time and puts a load on the server.

For anyone new to iSCSI here is a short description
iSCSI is a Storage Area Network rather then a network file system, think
of a Fibre Channel SAN but using IP and Gigabit Ethernet to deliver the
block level access rather than Fibre Channel.

http://whatis.techtarget.com/definition/0,,sid9_gci750136,00.html
or a google search
http://www.google.com/search?hl=en&q=iscsi&btnG=Google+Search

To the host it looks like any other SCSI disk which you create a standard
file system on. Partitions or LUNs are not usually accessed by more then
one host between unless you are using a special file system.

By centralising the storage away from the server you gain economies of
scale and manageability. Also if a server fails it's easy and very quick
to remount the partition on a different server  and resume service. There
is no need to move disks or cables between  servers, you might need to
update the SAN access rules to allow the new server to see the disk.
Backup can be easer if your storage array also includes features such as
snapshots.

Richard Westlake

School of Crystallography, Birkbeck College, Malet Street, London WC1E 7HX
Tel: 020-7631-6859
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               Truth endures but spelling changes    --  Anon.
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On Tue, 23 Nov 2004, Yiorgos Adamopoulos wrote:

> Date: Tue, 23 Nov 2004 13:39:09 +0200
> From: Yiorgos Adamopoulos <[email-masked]>
> To: [email-masked]
> Subject: MBX mailboxes over iSCSI
>

---

From: Guy Dawson <[email-masked]>
Date: Wed, 24 Nov 2004 10:20:34 +0000

> If that is the case, it *may* work if locking is solved.

Agreed! If iSCSI 'sits' in the same place as ATA, SATA, SCSI, Fibre
Channel etc. then locking should work over iSCSI. I'd still want to test
it a lot before rolling out a production server using it.

> those filesystems, it will not work.

Definatly agreed!

Guy

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From: Ralf Utermann <[email-masked]>
Date: Wed, 24 Nov 2004 14:02:54 +0100

Mark Crispin wrote:
[...]
> page to guarantee that updates were atomic across all users of the 
I am quite sure, that DCE/DFS would allow mbx. It is good, stable and 
mature
technology. End of service for IBMs DCE/DFS for AIX is April/2006. Sigh.

Bye, Ralf
-- 
         Ralf Utermann
_____________________________________________________________________
         Universität Augsburg, Institut für Physik   --   EDV-Betreuer
         Universitätsstr.1
         D-86135 Augsburg                     Phone:  +49-821-598-3231
         SMTP: [email-masked]         Fax: -3411

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From: Guy Dawson <[email-masked]>
Date: Thu, 25 Nov 2004 11:35:43 +0000

Ralf Utermann wrote:
>> even if the locking problem is solved.  The only network filesystem 
>> that I know of in which mbx would work was the old TOPS-20 from two 
>> decades ago, and only because that filesystem had rigorous token 
>> passing on a page to guarantee that updates were atomic across all 
>> users of the network filesystem.
> 

Off Topic Sigh indeed!

I used DCE/DFS when I was working at IBM Austin in 1993. Before that
I've used VAX/VMS 4.4 and later with VAXClusters. I'm too much of a
youth (not 40 yet!) to have used TOPS-20.

So, with a history of working, locking, distributed file system why
are we still struggling with NFS?

Guy, out