I am looking at using consolidated storage to ease our fragmented and
increasingly hard to manage storage problem at my company. The conventional
way to go seems to be to buy an expensive fibre channel SAN from HP or EMC,
buy FC cards for all the servers, dual FC switches, and an FC array with
dual redundant FC-SCSI controllers.

But iSCSI keeps popping up as a cheaper alternative what with using exsiting
giga infrastructure. I have done some tests with Linux and MS clients
connecting to simple a Linux target but there seem to be problems with using
this kind of thing operationally. The biggest one I find is redundancy.

Is it possible to make a fully redundant iSCSI disk storage array?
You can get SATA storage arrays on the market but they usually have a SCSI
connection and are not dual redundant. The SATA controller becomes a risk.
But even if that weren't the case, the array connector should somehow
connect to two server controllers to provide redundancy.

In short, I can see how to make an iSCSI storage array, put it on the
network, and get initiators to connect to it, but there would be very little
redundancy. There are several single points of failure on the storage array
which would preclude it from 24/7 mission critical use.

Anyone know of a way around this? Or am I going to have to wait for bespoke
iSCSI products to come to market?

[ Post a follow-up to this message ]

"Rob Scott" <rob.scott@fathomtechnology.com> wrote in
news:41066347@andromeda.datanet.hu:

> In short, I can see how to make an iSCSI storage array, put it on the
> network, and get initiators to connect to it, but there would be very
> little redundancy. There are several single points of failure on the
> storage array which would preclude it from 24/7 mission critical use.
>
> Anyone know of a way around this? Or am I going to have to wait for
> bespoke iSCSI products to come to market?

I'm not sure if it's out yet, but EMC are doing iSCSI targets on their
Symmetrix high-end storage. The network itself would have to be made
redundant, but how the iscsi initiators would use it, i don't know.

--
/Jesper Monsted

[ Post a follow-up to this message ]

On Tue, 27 Jul 2004 16:14:28 +0200, "Rob Scott"
<rob.scott@fathomtechnology.com> wrote:

>I am looking at using consolidated storage to ease our fragmented and
>increasingly hard to manage storage problem at my company. The conventional
>way to go seems to be to buy an expensive fibre channel SAN from HP or EMC,
>buy FC cards for all the servers, dual FC switches, and an FC array with
>dual redundant FC-SCSI controllers.
>
>But iSCSI keeps popping up as a cheaper alternative what with using exsitin
g
>giga infrastructure. I have done some tests with Linux and MS clients
>connecting to simple a Linux target but there seem to be problems with usin
g
>this kind of thing operationally. The biggest one I find is redundancy.
>
>Is it possible to make a fully redundant iSCSI disk storage array?
>You can get SATA storage arrays on the market but they usually have a SCSI
>connection and are not dual redundant. The SATA controller becomes a risk.
>But even if that weren't the case, the array connector should somehow
>connect to two server controllers to provide redundancy.
>
>In short, I can see how to make an iSCSI storage array, put it on the
>network, and get initiators to connect to it, but there would be very littl
e
>redundancy. There are several single points of failure on the storage array
>which would preclude it from 24/7 mission critical use.
>
>Anyone know of a way around this? Or am I going to have to wait for bespoke
>iSCSI products to come to market?
>

An iSCSI environment can be made just as redundant as a FC SAN
environment.  I can personally say that all aspects work with the
exception of the iSCSI failover.  We only briefly tested it on NetApp
and it appeared not to work.  Granted it was an ad hoc test with an
uncertain application but still.  I just can't vouch for it
personally.

~F

[ Post a follow-up to this message ]

On Tue, 27 Jul 2004 22:34:26 GMT, Faeandar <mr_castalot@yahoo.com>
wrote:

>On Tue, 27 Jul 2004 16:14:28 +0200, "Rob Scott"
><rob.scott@fathomtechnology.com> wrote:
> 
>
>An iSCSI environment can be made just as redundant as a FC SAN
>environment.  I can personally say that all aspects work with the
>exception of the iSCSI failover.  We only briefly tested it on NetApp
>and it appeared not to work.  Granted it was an ad hoc test with an
>uncertain application but still.  I just can't vouch for it
>personally.
>
>~F

I feel remiss in not mentioning the other pieces since the iSCSI
failover part is fairly significant... 

All the networking pieces can be made redundant.  Alot of people don't
realize that ethernet can be made as fail-proof as FC SAN's, it's just
that generally the size of an ethernet network is so much larger that
it's not cost justified in most cases.

However, NetApp iSCSI is *supposed* to failover fine, just like the
other protocols it handles.  It's even supposed to failover to a filer
that does not have an iSCSI license..

~F

[ Post a follow-up to this message ]

"Rob Scott" <rob.scott@fathomtechnology.com> wrote in message
news:41066347@andromeda.datanet.hu...
> I am looking at using consolidated storage to ease our fragmented and
> increasingly hard to manage storage problem at my company. The
conventional
> way to go seems to be to buy an expensive fibre channel SAN from HP or
EMC,
> buy FC cards for all the servers, dual FC switches, and an FC array with
> dual redundant FC-SCSI controllers.
>
> But iSCSI keeps popping up as a cheaper alternative what with using
exsiting
> giga infrastructure. I have done some tests with Linux and MS clients
> connecting to simple a Linux target but there seem to be problems with
using
> this kind of thing operationally. The biggest one I find is redundancy.
>
> Is it possible to make a fully redundant iSCSI disk storage array?
> You can get SATA storage arrays on the market but they usually have a SCSI
> connection and are not dual redundant. The SATA controller becomes a risk.
> But even if that weren't the case, the array connector should somehow
> connect to two server controllers to provide redundancy.
>
> In short, I can see how to make an iSCSI storage array, put it on the
> network, and get initiators to connect to it, but there would be very
little
> redundancy. There are several single points of failure on the storage
array
> which would preclude it from 24/7 mission critical use.
>
> Anyone know of a way around this? Or am I going to have to wait for
bespoke
> iSCSI products to come to market?
>
>

Have you considered Equallogic and Left Hand Networks? There are probably
other names that I am missing.  Also NetApp FAS2xx should be worth a look.
iSCSI boxes with redundancy and failover are expensive, but  you could still
save some money on HBAs and switches.

Also, if you decide for FC look beyond HP and EMC. Xiotech?

Good luck

Art

[ Post a follow-up to this message ]

Faeandar wrote:
> On Tue, 27 Jul 2004 16:14:28 +0200, "Rob Scott"
> <rob.scott@fathomtechnology.com> wrote:
>
> 
>
>
> An iSCSI environment can be made just as redundant as a FC SAN
> environment.  I can personally say that all aspects work with the
> exception of the iSCSI failover.  We only briefly tested it on NetApp
> and it appeared not to work.  Granted it was an ad hoc test with an
> uncertain application but still.  I just can't vouch for it
> personally.
>
> ~F

It is clear that the network components can easily do failover and
redundancy and so on. That is just down to simple networking.

The problem is what is attached to the network down to the disk drives.
If you just have a bunch of disks in a PC, even if you have a RAID array
for the disks, then the motherboard is a single point of failure.

You could have an external disk array connected via SCSI to two PCs in a
failover cluster confugeration.

Or you could put two identical iSCSI boxes on the net and RAID between them.

None of these solutions is at all ideal.

What you want to end up with is a SATA disk array, with redundant SATA
controllers (not seen it so far) and two ethernet ports. The disk can be
RAID anything you like.

I don't see anything like this on the market yet. The simple solution
gives you no redundancy past the ethernet port to the PC. Solutions with
dual failover clustered PCs or RAID over 2 iSCSI devices are either
tricky to implement or expensive (RAID 1 costs you double) or tricky to
administer (in the case of RAID over iSCSI).

[ Post a follow-up to this message ]

ahedge wrote:

> "Rob Scott" <rob.scott@fathomtechnology.com> wrote in message
> news:41066347@andromeda.datanet.hu...
> 
>
> conventional
> 
>
> EMC,
> 
>
> exsiting
> 
>
> using
> 
>
> little
> 
>
> array
> 
>
> bespoke
> 
>
>
> Have you considered Equallogic and Left Hand Networks? There are probably
> other names that I am missing.  Also NetApp FAS2xx should be worth a look.
> iSCSI boxes with redundancy and failover are expensive, but  you could sti
ll
> save some money on HBAs and switches.
>
> Also, if you decide for FC look beyond HP and EMC. Xiotech?
>
> Good luck
>
> Art
>
>

It looks to me that the LHN products do not have redundancy beyond
having dual NICs.
The Equallogic products may have.

Still looks like iSCSI has a way to go to be used for anything other
than non-critical storage. I wouldn't want to run critical email,
database, and other things on it if there wasn't dual redundancy.
If the thing went down because for example the processor board failed,
then the entire company would be brought to its knees if all the servers
got their storage from there.

Thanks for the pointers.

[ Post a follow-up to this message ]

Rob Scott wrote:

> It is clear that the network components can easily do failover and
> redundancy and so on. That is just down to simple networking.
>
> The problem is what is attached to the network down to the disk drives.
> If you just have a bunch of disks in a PC, even if you have a RAID array
>   for the disks, then the motherboard is a single point of failure.
>
> You could have an external disk array connected via SCSI to two PCs in a
> failover cluster confugeration.
>
> Or you could put two identical iSCSI boxes on the net and RAID between
> them.
>
> None of these solutions is at all ideal.
>
> What you want to end up with is a SATA disk array, with redundant SATA
> controllers (not seen it so far) and two ethernet ports. The disk can be
> RAID anything you like.

Does iSCSI mean your SAN box *must* use SCSI (or SATA) disks? If your
SAN box uses FC disks it can be made fully redundant right up to the
disks themselves, right? Your SAN box will still be very expensive but
your connections will be much cheaper when done with iSCSI over Gigabit
Ethernet.

B.

[ Post a follow-up to this message ]

"Rob Scott" <rob.scott@fathomtechnology.com> wrote in message
news:41066347@andromeda.datanet.hu...

...

> Is it possible to make a fully redundant iSCSI disk storage array?

I guess that the short answer would have to be 'no', unless you can find
SATA drives that have two connectors on them as high-end FC drives do:
otherwise, drive-interconnect or controller failure will always create
apparent drive failure in a manner that is not a problem in fully-redundant
FC storage.

On the other hand, if that can be discounted as a drawback a qualified
answer may be 'yes':  just use two completely redundant paths from host(s)
to separate iSCSI SATA arrays, and mirror between them.  Unfortunately, this
doesn't give you the kind of no-single-point-of-failure *box* that you can
purchase from people like EMC:  it requires the fail-over and mirroring
intelligence to reside in the host(s).

I'd think it would be possible to build an iSCSI box with EMC-style
redundancy at least up to the back-end disk controllers (and possibly even
to the final links to the disks, if SATA disks attached via SAS turn out to
be able to handle dual initiators), but (just as is the case with existing
FC fully-redundant boxes) some vendor would have to create such a
proprietary combination out of otherwise standard components.

- bill

[ Post a follow-up to this message ]

"Rob Scott" <rob_scott@epam.com> wrote in message
news:4108fa40@andromeda.datanet.hu...
> ahedge wrote:
> 
SCSI[vbcol=seagreen] 
risk.[vbcol=seagreen] 
probably[vbcol=seagreen] 
look.[vbcol=seagreen] 
still[vbcol=seagreen] 
>
> It looks to me that the LHN products do not have redundancy beyond
> having dual NICs.
> The Equallogic products may have.
>
> Still looks like iSCSI has a way to go to be used for anything other
> than non-critical storage. I wouldn't want to run critical email,
> database, and other things on it if there wasn't dual redundancy.
> If the thing went down because for example the processor board failed,
> then the entire company would be brought to its knees if all the servers
> got their storage from there.

I hear you, but I don't follow on the iSCSI-may-not-be-for-serious-business
path. I would not bet my company on a possibly failing board either.Also I
would not take chances on any  single array of disks, no matter how many
controllers are in it.

In your initial post you said: "I am looking at using consolidated storage
to ease our fragmented and increasingly hard to manage storage problem at my
company" .

I hear the  pain,  "increasingly hard to manage"  which is a good reason to
move away from what you have, but the "consolidated storage" part  seems to
indicate that you want to put everything on a single array. Well, if that's
the case, don't: it's a rather bad idea, with iSCSI, FC  or even plain SCSI.

Perhaps the answer is building your consolidated  storage layout with an eye
on failover  (BC, DR, whatever..)? We know that those things are going to
fail, so why not design  a failproof  network in the first place. After
that, choosing the pieces to build it should be a trivial  matter of
measuring the bang for the buck from each vendor/technology/product.

> Thanks for the pointers.

You're welcome, but I should have mentioned also Falconstor and Datacore,
two software only shops worth considering, especially  if your company has
already  spent beaucoup money  on hardware.

[ Post a follow-up to this message ]