NCQ vs TCQ performance?


T

Tom Forsmo

Hi

In an article about the performance of sata raid controllers (
StorageReview:
http://www.storagereview.com/articles/200406/20040625TCQ_1.html?page=0,5
) using NCQ or TCQ. it stated that TCQ is much faster than NCQ:

"SATA TCQ and SATA RAID have the potential to deliver benefits to the
server market just as great as those of SCSI TCQ and SCSI RAID."

So by using a SATA-1 TCQ RAID controller and WD Raptor disks one can get
close to SCSI performance. (Sata 2 does not actually give the same
performance according other tests I have read.)

The article was written in 2004, and in four years much may have
happened with NCQ. So the question is, does anybody know if much has
happened with NCQ? or can I still trust the articles conclusions in
terms of its performance?

regards

tom
 
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T

Tom Forsmo

Eric said:
TCQ was a disaster, it was built on top of a flawed attemp to make PATA
multitask.
I doubt anyone supports TCQ today, especially on SATA. Microsoft and
Intel do NOT.

Then I think you have been misinformed, some SATA disk support TCQ
exceptionally well, such as the WD Raptor disks. Paired with a TCQ sata
controller they outperform any NCQ disks on market. It actually comes
close to SCSI performance, which no NCQ disks is able of achieving. Mind
you this is with server type load. With single user load, the
performance is somewhat lower than with NCQ. The reason for that is
because TCQ is a more heavyweight protocol than NCQ, so you wont see a
gain until the load is increased somewhat.

You should read the entire article, it is quite interresting
StorageReview:
http://www.storagereview.com/articles/200406/20040625TCQ_1.html?page=0,5
NCQ performance varies from negative to positive compared to original IDE.
You have to find some recent benchmarks, including both controllers and
drives.

I have been looking around, and havent found much, neither benchmarks
nor info about NCQ updates.

regards

tom
 
A

Arno Wagner

In comp.sys.ibm.pc.hardware.storage Tom Forsmo said:
In an article about the performance of sata raid controllers (
StorageReview:
http://www.storagereview.com/articles/200406/20040625TCQ_1.html?page=0,5
) using NCQ or TCQ. it stated that TCQ is much faster than NCQ:
"SATA TCQ and SATA RAID have the potential to deliver benefits to the
server market just as great as those of SCSI TCQ and SCSI RAID."
So by using a SATA-1 TCQ RAID controller and WD Raptor disks one can get
close to SCSI performance. (Sata 2 does not actually give the same
performance according other tests I have read.)

WD makes this claim for some time now, because they do not have
SCSI disks. I think it is a marketing-lie.
The article was written in 2004, and in four years much may have
happened with NCQ. So the question is, does anybody know if much has
happened with NCQ? or can I still trust the articles conclusions in
terms of its performance?

I think you copuld not trust it 2004 and you cannot trust it now.

Arno
 
T

Tom Forsmo

Arno said:
WD makes this claim for some time now, because they do not have
SCSI disks. I think it is a marketing-lie.

If you had read the article I references, you would see they have made
measurements comparing the Raptor disk to both SCSI, SATA NCQ and SATA
non-NCQ. And the Raptor is by far the fastest disk of the SATA types,
for server type load. The results have been feed into a long standing
peformance table where you can compare different types of disks, both
SCSI and SATA types, if you sort it by performance, you will see SCSI
holding the top positions, the highest performant sata disk mentioned on
the list is the Raptor. After that you find the all the other SATAs.

But my question is, has anything changed with NCQ. But after having
studied it, I dont think any changes have occured. The NCQ
implementation is really only an implementation of the TCQ simple mode.
Simple mode alone gives some performance boost. The referenced article
shows that NCQ disk is more suited for desktop load, while TCQ is more
suited for server load. And that is why I suspect NCQ has not changed much.


regards

thomas
 
A

Arno Wagner

In comp.sys.ibm.pc.hardware.storage Tom Forsmo said:
Arno Wagner wrote:
If you had read the article I references, you would see they have made
measurements comparing the Raptor disk to both SCSI, SATA NCQ and SATA
non-NCQ. And the Raptor is by far the fastest disk of the SATA types,
for server type load. The results have been feed into a long standing
peformance table where you can compare different types of disks, both
SCSI and SATA types, if you sort it by performance, you will see SCSI
holding the top positions, the highest performant sata disk mentioned on
the list is the Raptor. After that you find the all the other SATAs.

I did not calim that the Raptor was slow. What WD has claimed, however,
time and again, is that the Raptor is just as good as an SCSI disk.
It is not. It is, of course, faster than slower spinning (S)ATA
drives, unless you are interessted primarily in linear performance.
But my question is, has anything changed with NCQ. But after having
studied it, I dont think any changes have occured.

I agree.
The NCQ implementation is really only an implementation of the TCQ
simple mode. Simple mode alone gives some performance boost. The
referenced article shows that NCQ disk is more suited for desktop
load, while TCQ is more suited for server load. And that is why I
suspect NCQ has not changed much.

It is also that on high-performance set-ups, the command reordering,
buffering, etc. is done by the OS anyways. In extreme cases (e.g.
an Oracle server) it is even done by the application. The disk can
add a little, but not that much.

Arno
 
T

Tom Forsmo

Arno said:
I did not calim that the Raptor was slow. What WD has claimed, however,
time and again, is that the Raptor is just as good as an SCSI disk.
It is not.

I have never heard the WD marketing slogans. In any case, anyone knows
that marketing is about exaggerating facts. Its always been that way, so
if they have claimed its as fast?/good? as SCSI, its just marketing,
otherwise we wouldn't need SCSI any more.

But SCSI has other qualities which the Raptor or other SATAs does not
have. E.g. SCSI scales with the load, which the Raptor does not. The
Raptor only excels when the queue is larger than 16 commands, SCSI
handles queues lower than that quite nicely in contrast. SCSI is also
more stable, reliable and can handle top loads more stable than sata
disks can.
It is, of course, faster than slower spinning (S)ATA
drives, unless you are interessted primarily in linear performance.

What you are saying is that the only reason the raptor is faster is
because of the spindle speed. which is not correct. Its is also faster
because it uses TCQ instead of NCQ. But as stated, only for server loads.

regards

tom
 
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A

Arno Wagner

Arno Wagner wrote:
I have never heard the WD marketing slogans. In any case, anyone knows
that marketing is about exaggerating facts. Its always been that way, so
if they have claimed its as fast?/good? as SCSI, its just marketing,
otherwise we wouldn't need SCSI any more.
True.

But SCSI has other qualities which the Raptor or other SATAs does not
have.

Also true.
E.g. SCSI scales with the load, which the Raptor does not. The
Raptor only excels when the queue is larger than 16 commands, SCSI
handles queues lower than that quite nicely in contrast. SCSI is also
more stable, reliable and can handle top loads more stable than sata
disks can.

Agreed. SCSI also has multi-master capabilities and some other nice
functional featuires.
What you are saying is that the only reason the raptor is faster is
because of the spindle speed. which is not correct.

No, that is not what I am saying. True, latency plays a role, but...
Its is also faster because it uses TCQ instead of NCQ. But as
stated, only for server loads.

... as you say. For mostly linear accesses TCQ/NCQ daoe not
play a role and the lower bit density of the Raprors (and
SCSI drives) slow them down to SATA comparable speeds.

I expect by server loads you mean database loads, webserver
loads and the like, i.e. multiple smaller reads from,
potentially from different processes. Then the queuing
model and latency are certainly or primary interest.

Arno
 
T

Tom Forsmo

Arno said:
No, that is not what I am saying. True, latency plays a role, but...


.. as you say. For mostly linear accesses TCQ/NCQ daoe not
play a role and the lower bit density of the Raprors (and
SCSI drives) slow them down to SATA comparable speeds.

What do you mean by linear access, do you mean sequential
reading/writing (as in reading/writing a large file in one)?
I expect by server loads you mean database loads, webserver
loads and the like, i.e. multiple smaller reads from,
potentially from different processes. Then the queuing
model and latency are certainly or primary interest.

By server loads I mostly mean concurrent access by different
threads/processes, which includes file access, database and so on. How
high the load is, is not as interesting. Both servers and desktops can
have a high load, but only servers will have a high concurrency level.

So by putting the two comments togheter, what you are saying is that the
Raptor is slower because sequntial read/write only as fast or slower
than an ordinary NCQ disk? That is correct, but only in it self. The
Raptor is designed to be an cheaper entry level server disk, not a
desktop disk. So by that, the Raptor is faster, but only for server
loads. If you use it in a desktop system its seems to be slower than an
ordinary NCQ disk and that is because of the TCQ protocol overhead which
in a SATA system does not scale as well as it does in a SCSI system.

If one wants really fast disk access no matter what, I would go for a
complete SCSI system. But SCSI is 3-5 times more expensive, in addition
SCSI do not have as large disks as ATA does, at least which is as cheap.

tom
 
A

Arno Wagner

What do you mean by linear access, do you mean sequential
reading/writing (as in reading/writing a large file in one)?
Yes.
By server loads I mostly mean concurrent access by different
threads/processes, which includes file access, database and so on. How
high the load is, is not as interesting. Both servers and desktops can
have a high load, but only servers will have a high concurrency level.

A Linux desktop can have high concurrency at high load without
trouble, if the user is compent. That this is rather rare under
Windows gets no argument from me.
So by putting the two comments togheter, what you are saying is that the
Raptor is slower because sequntial read/write only as fast or slower
than an ordinary NCQ disk? That is correct, but only in it self. The
Raptor is designed to be an cheaper entry level server disk, not a
desktop disk.

Agreed. It is however often mistaken as a blazingly fast desktop
"enthusiast" disk, which it is not.
So by that, the Raptor is faster, but only for server loads.
Exactly.

If you use it in a desktop system its seems to be slower than an
ordinary NCQ disk and that is because of the TCQ protocol overhead which
in a SATA system does not scale as well as it does in a SCSI system.
If one wants really fast disk access no matter what, I would go for a
complete SCSI system. But SCSI is 3-5 times more expensive, in addition
SCSI do not have as large disks as ATA does, at least which is as cheap.

Actually with modern OSes, often getting more RAM wil help a lot.
For larger storage needs SCSI/SAS is the way to go. For smaller
ones were low throughput on writes is acceptable, FLASH drives
may also be an option. If the sustained write rate is low, writes
can be speed up by more available RAM.

But I agree, if you just want to change one thing, going to
SCSI/SAS will give a significant boost with many practical loads.
And if you make it RAID with a really good controller, you will
also get better throughput (for RAID1 only on reads).

Arno
 
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N

Nicola Taibi

Tom said:
Hi

In an article about the performance of sata raid controllers (
StorageReview:
http://www.storagereview.com/articles/200406/20040625TCQ_1.html?page=0,5
) using NCQ or TCQ. it stated that TCQ is much faster than NCQ:

"SATA TCQ and SATA RAID have the potential to deliver benefits to the
server market just as great as those of SCSI TCQ and SCSI RAID."

So by using a SATA-1 TCQ RAID controller and WD Raptor disks one can
get close to SCSI performance. (Sata 2 does not actually give the same
performance according other tests I have read.)

The article was written in 2004, and in four years much may have
happened with NCQ. So the question is, does anybody know if much has
happened with NCQ? or can I still trust the articles conclusions in
terms of its performance?

regards

tom
Maybe it can help:
http://www.hardwaresecrets.com/article/315/1

With my best regards,

--
Nicola Taibi
Web home page: http://whisky1767.altervista.org
Photo home page: http://community.webshots.com/user/ntaibi
Nikon photo album: http://www.nikonista.it/ntaibi
e-mail: (e-mail address removed)
 

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