Re: [NOVICE] - SAN/NAS/DAS - Need advises

Hi all,

I am working on upgrading my hardware and wondering how Postgres could
work with SAN, NAS and DAS .
Can someone advise me or share experiences ?

Regards,
Fel

On Tue, 7 Sep 2010 15:03:44 +0200, fel <fellsin(at)hotmail(dot)com> wrote:
> Hi all,
>
> I am working on upgrading my hardware and wondering how Postgres could
> work with SAN, NAS and DAS .
> Can someone advise me or share experiences ?

Unless you want to spend *A LOT* of money, DAS is the way to go. You can
get quite a bit of the same functionality without the financial overhead
from the use of a volume manager + DAS.

JD

>
> Regards,
> Fel

--
PostgreSQL - XMPP: jdrake(at)jabber(dot)postgresql(dot)org
Consulting, Development, Support, Training
503-667-4564 - http://www.commandprompt.com/
The PostgreSQL Company, serving since 1997

On Tue, Sep 7, 2010 at 9:42 AM, Joshua D. Drake <jd(at)commandprompt(dot)com> wrote:
> On Tue, 7 Sep 2010 15:03:44 +0200, fel <fellsin(at)hotmail(dot)com> wrote:
>> Hi all,
>>
>> I am working on upgrading my hardware and wondering how Postgres could
>> work with SAN, NAS and DAS .
>> Can someone advise me or share experiences ?
>
> Unless you want to spend *A LOT* of money, DAS is the way to go. You can
> get quite a bit of the same functionality without the financial overhead
> from the use of a volume manager + DAS.

With the right supplier, you can plug in literally 100 hard drives to
a regular server with DAS and for a fraction of the cost of a SAN.

--
To understand recursion, one must first understand recursion.

On 2010-09-07 20:42, Scott Marlowe wrote:
> With the right supplier, you can plug in literally 100 hard drives to
> a regular server with DAS and for a fraction of the cost of a SAN.
>
Ok, recently I have compared prices a NexSan SASBeast with 42 15K SAS drives
with a HP MDS600 with 15K SAS drives.

The first is 8gbit Fibre Channel, the last is 3Gbit DAS SAS. The
fibre channel version is about 20% more expensive pr TB.

So of course it is a "fraction of the cost of a SAN", but it is a
fairly small one.

--
Jesper

On 9/7/10 12:06 PM, Jesper Krogh wrote:
> On 2010-09-07 20:42, Scott Marlowe wrote:
>> With the right supplier, you can plug in literally 100 hard drives to
>> a regular server with DAS and for a fraction of the cost of a SAN.
> Ok, recently I have compared prices a NexSan SASBeast with 42 15K SAS drives
> with a HP MDS600 with 15K SAS drives.
>
> The first is 8gbit Fibre Channel, the last is 3Gbit DAS SAS. The
> fibre channel version is about 20% more expensive pr TB.
>
> So of course it is a "fraction of the cost of a SAN", but it is a
> fairly small one.

Are you really comparing equal systems? "8gbit Fibre Channel" means a single Fibre Channel shared by 42 disks, whereas "3GBit DAS SAS" means 42 3gbit channels running in parallel. It seems like you'd really need some realistic benchmarks that emulate your actual server load before you'd know how these two systems compare.

Craig

Hi everybody,

I have been reading this thread and I got the idea that
SANs to avoid, but would somebody please give a bit of
Comparison/perspective on NAS?

Regards,

Tena Sakai
tsakai(at)gallo(dot)ucsf(dot)edu

On 9/7/10 12:36 PM, "Craig James" <craig_james(at)emolecules(dot)com> wrote:

> On 9/7/10 12:06 PM, Jesper Krogh wrote:
>> On 2010-09-07 20:42, Scott Marlowe wrote:
>>> With the right supplier, you can plug in literally 100 hard drives to
>>> a regular server with DAS and for a fraction of the cost of a SAN.
>> Ok, recently I have compared prices a NexSan SASBeast with 42 15K SAS drives
>> with a HP MDS600 with 15K SAS drives.
>>
>> The first is 8gbit Fibre Channel, the last is 3Gbit DAS SAS. The
>> fibre channel version is about 20% more expensive pr TB.
>>
>> So of course it is a "fraction of the cost of a SAN", but it is a
>> fairly small one.
>
> Are you really comparing equal systems? "8gbit Fibre Channel" means a single
> Fibre Channel shared by 42 disks, whereas "3GBit DAS SAS" means 42 3gbit
> channels running in parallel. It seems like you'd really need some realistic
> benchmarks that emulate your actual server load before you'd know how these
> two systems compare.
>
> Craig
>

On Tue, Sep 7, 2010 at 1:36 PM, Craig James <craig_james(at)emolecules(dot)com> wrote:
> On 9/7/10 12:06 PM, Jesper Krogh wrote:
>>
>> On 2010-09-07 20:42, Scott Marlowe wrote:
>>>
>>> With the right supplier, you can plug in literally 100 hard drives to
>>> a regular server with DAS and for a fraction of the cost of a SAN.
>>
>> Ok, recently I have compared prices a NexSan SASBeast with 42 15K SAS
>> drives
>> with a HP MDS600 with 15K SAS drives.
>>
>> The first is 8gbit Fibre Channel, the last is 3Gbit DAS SAS. The
>> fibre channel version is about 20% more expensive pr TB.
>>
>> So of course it is a "fraction of the cost of a SAN", but it is a
>> fairly small one.
>
> Are you really comparing equal systems?  "8gbit Fibre Channel" means a
> single Fibre Channel shared by 42 disks, whereas "3GBit DAS SAS" means 42
> 3gbit channels running in parallel.  It seems like you'd really need some
> realistic benchmarks that emulate your actual server load before you'd know
> how these two systems compare.

Well, not usually. Most SAS DAS systems use a single multi-lane cable
that gives you 4x3GB channels, etc.

However, unless you're doing little than sequentially scanned reports
of a large size being read, the difference between 8gb and 3gb is not
going to matter. There are lots of very hard working transactional
databases that are lucky to see more than 20 or 40 megabytes a second
getting trasnferred spread out over 30 or 40 drives.

What really matters here is if the 8gb SAN is as fast as or faster
than the DAS setup. For most people measuring the speed of the
interface is a lot like the famous Tom Lane quote about benchmarking
jet fighters versus airliners by measuring the amount of runway they
need.

If you can get 10k tps on the SAN and 10k tps on the DAS

So to the OP, what are hoping to get from the SAN that you won't get
from the DAS? Also, how reliable are these two in comparison to each
other is kinda of important. Speed of the interface isn't a real big
deal for a database server Size of the battery backed cache in each
one is And how each survives the power plug pull test. If your SAN
salesman balks at a power on test you don't have to run it, you'll
know.

--
To understand recursion, one must first understand recursion.

On 2010-09-07 22:47, Scott Marlowe wrote:
> Ok, recently I have compared prices a NexSan SASBeast with 42 15K SAS
>>> drives
>>> with a HP MDS600 with 15K SAS drives.
>>>
>>> The first is 8gbit Fibre Channel, the last is 3Gbit DAS SAS. The
>>> fibre channel version is about 20% more expensive pr TB.
>>>
>>> So of course it is a "fraction of the cost of a SAN", but it is a
>>> fairly small one.
>>>
>> Are you really comparing equal systems? "8gbit Fibre Channel" means a
>> single Fibre Channel shared by 42 disks, whereas "3GBit DAS SAS" means 42
>> 3gbit channels running in parallel. It seems like you'd really need some
>> realistic benchmarks that emulate your actual server load before you'd know
>> how these two systems compare.
>>
> Well, not usually. Most SAS DAS systems use a single multi-lane cable
> that gives you 4x3GB channels, etc.
>
> However, unless you're doing little than sequentially scanned reports
> of a large size being read, the difference between 8gb and 3gb is not
> going to matter. There are lots of very hard working transactional
> databases that are lucky to see more than 20 or 40 megabytes a second
> getting trasnferred spread out over 30 or 40 drives.
>
> What really matters here is if the 8gb SAN is as fast as or faster
> than the DAS setup. For most people measuring the speed of the
> interface is a lot like the famous Tom Lane quote about benchmarking
> jet fighters versus airliners by measuring the amount of runway they
> need.
>
If you can get 10k tps on the SAN and 10k tps on the DAS
> So to the OP, what are hoping to get from the SAN that you won't get
> from the DAS? Also, how reliable are these two in comparison to each
> other is kinda of important. Speed of the interface isn't a real big
> deal for a database server Size of the battery backed cache in each
> one is And how each survives the power plug pull test. If your SAN
> salesman balks at a power on test you don't have to run it, you'll
> know.
>
All wise words, that I can acknowledge with "hands on" experience.

I was basically only reacting to the "you can do the choice based
on cost alone.. DAS is soo-much-cheaper". In the comparison, I get
an equal amount of disks with same characteristica, in the same
raid-configuration. 1-2GB Battery backed cache on each. So on
paper, I think the systems are directly comparable. In the real
world it is more about "feelings" since I never get to benchmark both of
them.

Jesper
--
Jesper

* Scott Marlowe <scott(dot)marlowe(at)gmail(dot)com> wrote:

> What really matters here is if the 8gb SAN is as fast as or faster
> than the DAS setup. For most people measuring the speed of the
> interface is a lot like the famous Tom Lane quote about benchmarking
> jet fighters versus airliners by measuring the amount of runway they
> need.

If you really want to know what's better, you'll have to test the
candidates with real loads: record your real runtime load w/ blktrace
and replay them on the candidates.

Nominal performance parameters as insufficient as a dd or iobench test.

For example, take an IBM XIV or DS8k w/ thin provisioning: simply
writing zeros (or just the same pattern to all blocks) will give you
almost the raw bus speed (maybe adding a little bit overhead inside
the storage system), since spindles will idle. Caches (bein RAM or
SSD) can make the storage look way faster than it really is (in rare
cases, bad cache decisions could make also make it slower).

Synthetic tests don't allow you to predict how spindle seeks, bus
jams, etc will behave in real production. It *heavily* depends on
your workload which storage type (and concrete product) will perform
in production, nominal parameters are too vague for enterprise usage.
(no, you can't even tell that DAS is faster than SAN).

You need to test your workload and then decide which product to use.

cu
--
----------------------------------------------------------------------
Enrico Weigelt, metux IT service -- http://www.metux.de/

phone: +49 36207 519931 email: weigelt(at)metux(dot)de
mobile: +49 151 27565287 icq: 210169427 skype: nekrad666
----------------------------------------------------------------------
Embedded-Linux / Portierung / Opensource-QM / Verteilte Systeme
----------------------------------------------------------------------

* Tena Sakai <tsakai(at)gallo(dot)ucsf(dot)edu> wrote:

Hi,

> I have been reading this thread and I got the idea that
> SANs to avoid, but would somebody please give a bit of
> Comparison/perspective on NAS?

same as for SAN: measure it on your real workload and compare
different products w/ similar stability and accessibility properties.

cu
--
----------------------------------------------------------------------
Enrico Weigelt, metux IT service -- http://www.metux.de/

phone: +49 36207 519931 email: weigelt(at)metux(dot)de
mobile: +49 151 27565287 icq: 210169427 skype: nekrad666
----------------------------------------------------------------------
Embedded-Linux / Portierung / Opensource-QM / Verteilte Systeme
----------------------------------------------------------------------