Will Cache on a RAID controller give a lower througput

[hcforde]

This is on an ASUS MB P5WDG2-ws-pro an Adaptec Dual Channel 2200s/64 in a PCI-X slot. The drives are fijitsu mas3184nc. There are no jumpers on the drives.

In HDTACH 3.0, I am getting about the same with 2 drives stripped as with one alone.

Single drive = Burst stripped is 135MB/sec sustained about 59 MB/sec
2 stripped = burst 138MB/sec and sustained 69MB sec
4 stripped = burst 139MB/Sec and sustained 69MB/sec
So no benefit from 4 drives stripped.

My thought is that the data has to go through the cache first which is not measured by the benchmarking program. Because of this "LAG" in data transfer to and from the disk the throughput may seem lower than it really is. Stated in another way, the 64MB cache is filling up first then the prog. measures what is left in the time frame it takes therefore to the program is seems like less data is being transferred.

What say ye?
Thanks

 

[Mondoman]

Cache won't lower throughput, as it is ridiculously fast compared with the physical data read/write process. Your "burst" numbers probably measure the max SCSI interface speed in practice. Not sure if your "sustained" numbers are sequential or random reads. Are you running RAID 5 or something like 0+1 for the 4 drives?
You need to be careful to figure out exactly what you're measuring in these sorts of situations. The PCI-X bus has some maximum throughput, the Adaptec card has some maximum throughput, the SCSI bus has some maximum throughput, and the SCSI drives have maximum throughput. Max values for the drives, SCSI, and PCI-X can be found; not sure what the max throughput of the Adaptec card is under RAID 5 or whatever RAID you're running. The point is, you need to do some research and calculations to figure out what part of the system is the bottleneck before you can think about what to do to minimize that bottleneck.
I would expect that running a 2nd SCSI drive/string off the same controller might very well reduce the throughput of the 1st string that you are benchmarking.


PS - Zebras and RAID drives are "striped".

 

[hcforde]

These are simply stripped-RAID 0. U320 dual RAID controller(per channel) & U320 drives!!!

The card is a 66Mhz card 64 bit that should give me a theoritical bandwidth limitation of over 500MB/Sec. in a PCI-X slot

The HDD's range from 90-115MB/Sec each


I am doing the stripped only because the RAID 10 was in the tank so I wanted to see if I had a faulty drive in the system. NOPE-unless they all are faulty at the same level.

I am beginning to think there is something wrong with the controller but I do not have another U320 controller to test with?

 

[Mondoman]

...
The card is a 66Mhz card 64 bit that should give me a theoritical bandwidth limitation of over 500MB/Sec. in a PCI-X slot

However, since the SCSI max bandwidth is only 320 MB/s, then that would be limiting over the PCI-X bandwidth. I don't know what percent of max SCSI bandwidth you should expect to achieve in real life. The 140MB/s bursts might represent your maximum effective bandwidth on the SCSI bus.
In addition, you mentioned in your other thread that you had another SCSI drive/string on the controller's other channel. That would be likely to reduce the max throughput on this channel, unless the card's controller can handle BOTH SCSI channels at max speed simultaneously.
Since the card's controller runs at 100MHz according to Adaptec, perhaps it can't handle even 320 MB/s. Perhaps the 140MB/s represents the controller's limit?

The HDD's range from 90-115MB/Sec each

In what test (i.e. under what conditions: reading/writing/both? file size? total transfer? and so forth)?

 

[Mondoman]

Here's an article with some nice comparison charts:
http://www.wwpi.com/worldwide/LSI_1205_final.pdf

 

[hcforde]

1. This is 320MB/sec per channel - that is how all controllers are rated-per channel

2. The range(90-115 MB/sec) is what the manufacturer Fujitsu gives in its specs for this drive

3. With 4 drives I should approach at least 80-85% of the limit of the controller channel but I seem to be reaching a ceiling somewhere.

4. doing the math gives me 500+MB/sec over the PCI-X bus that would include both controlers channels

5. the one controller channel is limited to 320 MB/sec

The problem is that I am geting bowhere close. Everything is ther for performance but it is not coming through(literally)

My focus in now on the controller itself-is it faulty? That is the most logical explanation at this point after I do one more thing.


ADAPTEC 2200s/64 card specs
Benefits
Low-profile MD2 design ideal high-density server & workstation solution, 64-bit/66 MHz PCI
Key Differentiators
Optimized Disk Utilization
RAID Level Migration
Online capacity expansion
Background initialization (for immediate RAID availability)
S.M.A.R.T. and SAF-TE support
Hot-swap disk drive support for easy replacement
Hot-spare disk support with automatic rebuild
Supports bootable arrays

Customer Needs
Ideal for entry-level to mid-range and high-density servers and workstations requiring up to 30 disk drives
System Environment
Mid-range SCSI servers and workstations, conventional and rackmount
Cache Memory
64 MByte (onboard)
RAID Levels
0, 1, 10, 5, 50, JBOD
Key RAID Features
Optimized disk utilization
Online RAID Level Migration
Online capacity expansion
Immediate RAID availability (background initialization)
S.M.A.R.T. support
SES/SAF-TE support
Number of devices
Up to 30 SCSI devices (15 per channel)
Bus System Interface Type

64-bit/66MHz PCI
External Connectors
Two 68-pin VHDCI
Internal Connectors
Two 68-pin high-density
Data Transfer Rate
Up to 320 MB/sec per channel
System Requirements
Available 5 volt or 3.3 volt, PCI 2.2complaint PCI slot
Package Contents
Adaptec SCSI RAID 2200S card
Low-profile bracket (in addition to the full-size bracket attached to the controller)
One 5-position, Ultra320 SCSI 68-pin high-density LVD Adaptec internal cable with active terminator
Quick Installation Guide booklet
Bootable CD-ROM w/RAID Management software and device drivers and documentation

Warranty
3 years

 

[hcforde]

THANKS,

Thats www.wwpi.com/worldwide/LSI_1205_final.pdf is what I'm talking about!!! That 270mb/CHANNEL IS MY 80-85%

My 4 drive are not coming anywhere close

Thank again

 

[Gazz-]

I have the same issue, have you found a solution yet ?

My Problem

Cheers,

Gazz-

Apologies, should have probably posted on your other thread regarding the problem you are getting.

 

[hcforde]

With the scores you are getting you are making me feel better -at your own expense. I have not found a solution. I am considering getting a PCI-E scsi card but that means bucks unless I can snag one from a Dell surplus guy here in Austin. I noticed you were using Dell stuff Do you live in Austin? Then again that may be why it is surplus. Works but not 100%.

If you read that article I posted there seems to be better benches than what we are getting. I am going to try to contact the author of the article and see if he has any ideas. One thing I found interesting was that he said that the max throughput on PCI-X or PCI-E was the same because they are basically using a PCI-X bridge chip to make RAID work on a PCI-E platform. Maybe that is why Adaptec has not announced any PCI-E raid cards. Anyway 3 and 4 slot PCI-E MB's are becomming more mainstream So I may do that to try and solve the problem.

The comment about the small files doesn't totally make sense to me. I am aware the you really want higher I/O's on small files but with lower sequential sustained reads are you getting it? Isn't that what SCSI and RAID is to excel at?


Frustrating isn't it

hcforde

 

[Gazz-]

Nope I'm not from Texas im in the UK.

The problem is very frustrating but I've given up on it

Im still using the card and RAID0 setup for my mythtv box and it works fine but it bugs me I'm not getting the best out of the hardware. If I had another PC which supported 64bit PCI cards I would test it on this but unfortunatly I don't. I will get another Ultra Wide 320 drive for the setup in time to see if this improves things but I don't know if it will.

If you ever figure this out please post back

Cheers,

Gazz.