View Full Version : Cache Segments

01-31-2002, 04:36 PM
I was reading the SoftRAID performance tips and found the following:

"Cache Segments - Most SCSI drives are preoptimized and never need adjustment with the number of cache segments. Typically, you would see "zero" as a setting, which allows a drive to use its defaults. A low number of cache segments is also good (e.g. 3), if the drive does not accept "0" as a setting. Many Seagate drives are preset to 16 cache segments, which is optimized to Windows, and actually perform relatively poorly on Mac OS systems."

I checked my striped array- 2 x ST318452LW Cheetahs- and the cache segments were set at 28. I tried to change it to 0 but the dialog box wouldn't allow the change to be saved. Is this something that needs to be set when setting up the volume? Or perhaps the '28' is the drves' default, and therefore the optimum setting (?). As to the last part of above- what would the optimal Mac setup?

01-31-2002, 05:45 PM
I think the higher number of cache segments allows the drive to deal with smaller files faster. One large cache segment would probably allow the drive to deal with bigger files faster.

Does softRAID allow you to change this?

I would think you would probably want from 3 to 10 cache segments per drive - NOT 28. I assume this is a per drive setup.

Try something other than zero.

QuickBench can show you how the drive or RAID deals with small files - 8KB to 10MB - it even has a graph for files from 8KB to 1024KB (1MB).

Kaye has a lot of experience with this. He should be able to shed more light. There have been concerns that the new Cheetahs (x15G2) do not perform as well as they should. I did not read those threads - so it could have had more to do with the SCSI card than the drive itself. Also SoftRAID wont be native on X until April....

At least they set a date http://macgurus.com/infopop/emoticons/icon_smile.gif

I'm back!

01-31-2002, 08:41 PM
I leave the G2 X15 (ST318452LW) at 28 cache segments for its 8MB onboard cache. The drive does very well at that number. I did not try different settings because I did run an exhaustive set of tests on the G1 X15 (ST318451LW) with its 4MB onboard cache at, if I recall correctly, its default 20 cache segments. I tried 1-30+ (can't remember exactly where I stopped) cache segments and found 24 the best for that drive.

I tested with ATTO bench test at 8MB, Sample Size 2, no System Disk Cache. Takes a very long time. k

01-31-2002, 09:27 PM
Well based on that extensive testing of yours, I'll take your advice, Kaye and leave things at 28. I assume that would be good for larger graphic files as well?

Dragon- welcome back and what's with the 'junior'?-
I was successful changing the cache segment number to 1- but now it won't let me change it back to 28!
I cannot perceive any differance in performance between these 2 settings when opening graphic files.....

I have noticed an apparent lag time (before fooling with the cache segments) when opening an existing file residing on the raided scsi drives. The G4 seems to take alot of time to locate the file. Once it finds it, it cranks it open in a hurry. Is this my imagination? It almost seems like files on the IDE drives are found more quickly...

[This message has been edited by gmidd (edited 31 January 2002).]

01-31-2002, 10:23 PM
How strange.. I was able to change the cache segments to 10 for each drive by changing them from 1 to 2 to 4 to 8 to 10. I could not change directly to a higher number- still won't let me change to 28 http://www.macgurus.com/ubb/confused.gif

01-31-2002, 11:25 PM
Hey gm,

Kind of a funny deal with SoftRaid, it will not allow you to set more than 10 cache segments . At least in my experience with Seagate drives. You can access mode pages and change this setting to anything with FWB Hard Disk Speed Tools and some other utilities. K has done ALOT of testing with standard benchmark tools, but if you think about it, Draggie's advice makes sense. A cache segment is how much data will be pre-fetched in the tracks beyond your small data file or how much of your huge file will be cached at one time. If you work at Pixar Studios running movie files on your Mac all day, you probably want 1-4 segments for nonlinear editing; if you work at an accounting firm, you probably want 28 segments for rapid-fire access to multiple small data bits. For most of us, somewhere between 4-8 segments with a 2MB cache, 8-16 segments with a 4 MB cache and 16-28 segments with an 8 MB cache will probably be optimal. Just my best guess.

[This message has been edited by MacMikester (edited 31 January 2002).]

01-31-2002, 11:26 PM
The SCSI forums and a few other posts went south one day. So did my main account. I was getting by on an old account - I could not even sign backup as myself for a while (3 days?), but now I am me and if young so much the better.

I assume you are running in classic Mac OS. I wonder if those cache modes/settings would have a bigger effect on 10.1?

SCSI is a more complex protocol and can be slower for small files. I would imagine you have a PCI SCSI card on a new world mac.

Also if your disk cache is one - the cache settings of the Cheetahs may not matter that much. There are lots of caches around but where is my money? http://macgurus.com/infopop/emoticons/icon_wink.gif

01-31-2002, 11:52 PM

To get back to 28 cache segments or anything over 10 or 11, I think MM is correct at 10 with SoftRAID, you need something like the HDT package and specifically FWB Configure. Mode Page 8 is the page that will allow you to change the number to higher than 10. My memory sucks but a Seagate Tech told me the G1 X15 (ST318451LW) could be set up to 50 something cache segments. I never went that high because I could see that the performance was decreasing well before I was near that.

BTW, my HDT is version 4. I never upgraded to 5 or whatever is current now. But version 4 of FWB Configure works just fine with OS9.2.2, just in case you also are not current. k

02-01-2002, 01:21 AM
The gurus warning page against FWB HDT not withstanding, it sounds like some of you use it on a regular basis. I wonder if those parameters can be reset without changing the drivers from softRAID to HDT-
Sounds like I'll need a setting around 16-24...
It appears the latest version of HDT is 4.5.
Not having used it before, anything in particular I should be wary of with the FWB product?

I like your positive outlook Drag!
fyi: Quicksilver733 ATTO UL3S 2x X15's, 2 x ibm60GXP IDE's running 9.2.2 and 10.1.2
Look forward to seeing my cheetahs on the X desktop someday... http://www.macgurus.com/ubb/rolleyes.gif

[This message has been edited by gmidd (edited 01 February 2002).]

02-01-2002, 07:35 AM
Actually, what do I need another $130 utility for anyway, when I can probably initialize the disk and reset the default params on it anyway. This kinda ticks me off. There's absolutely zilch on this topic in any of the softRAID literature accompanying their product. The only place I found the info I quoted earlier was on their website -and nowhere does it mention your choice is from 1 to 10.

02-01-2002, 10:42 AM
Well no go on resetting to defaults by initializing with....since I can set between 1 and 10 (w/ softRAID), this will require a little more planning as to how best to use these drives, which files to put on them, etc.
Now for another round of testing.

[This message has been edited by gmidd (edited 01 February 2002).]

02-01-2002, 10:48 AM
Right. Initializing a drive does not reset Mode Page Parameters. Only way to change MPP is with a utility that can access them. And you need to be careful what you change. But changing the cache segments on Mode Page 8 is a no-brainer.

I wrote an email to SoftRAID way back when the G1 X15 appeared with its default cache segments greater than SoftRAID would allow. Hopefully the next SoftRAID update will also address that issue. k

02-01-2002, 10:57 AM

Check your email. k

02-01-2002, 11:52 AM
There is an option in ATTO ExpressPro Tools to reset to factory defaults I believe but don't know about cache segments. I use FWB HDT 4.5.2 for my two 2G X15 and another Atlas 10k-3. The Atlas - using FWB Configure doesn't show the number of cache segments but does show 28 for those cheetahs.

I got the 4.5 upgrade from 4.0 for $15... more than worth it for good support in OS X and 9.2.2 and full support for $1000 worth of disks. It was also (4.5) the ONLY utility that allowed me to take a failed driver install (HDST 3.4 - will NEVER touch that piece of software again!) on a drive and restore it to factory defaults and allow it to be formatted. I also prefer it for taking over a SoftRAID drive to put Drive Setup rather than ExpressPro. I've used FWB for 10 yrs maybe? so it has been pennies. Less than keeping up with Norton, MicroMat, etc.

Still looking forward to SoftRAID-X and ExpressStripe 1.1...

02-01-2002, 12:46 PM
I also would testify to FWBs maturity. It will effectively knock out any other utilities screw ups with ease. FWB HDT also saved me from a SpeedTools disaster. The qualities in Softraid products are many so don't get the impression I don't like the product.

My biggest issue today will be replacing ALL the utilities that years of purchases have produced for OS9 that now need OSX versions. It will be very hard for all of us tinkerers to pick and choose amongst what will soon be a plethora of competing developers products. Worst part is, for awhile, just like OSX, the claims will always be that the utility is a 'work in progress' and we'll be unable to judge its usefulness for months to come. argh.

Good luck with your cache setting problem.(and Softraid fiasco) I am impressed with your tenacity. If I had to put a number on the percentage of people who even know what a mode page is, let alone who 'tamper' with them it makes you one in a million. (a conversation I have with my poor wife frequently trying to justify how 'special' I must be as I (ignorantly)'tamper' with such things...HAH).

Now to see what I can turn into random electrons............

[This message has been edited by ricks (edited 01 February 2002).]

02-01-2002, 09:18 PM
Thank you Kaye, for the mail.

Well Rick, I tried to explain the issue to my daughter who was tugging at my sleeve to get the hell off the computer- she just rolled her eyes and told me to stop screwing with it and leave well enough alone. And granted, from a perceptual standpoint, I'm hard pressed to be certain of any real-world performance change with differant settings of the cache segments...
But really, I just want to make sure I'm getting the most out of this expensive equipment!

Thanks Rick and Gregory, for more details on HDT. I can see now that qualified power users consider it a legitimate alternative to SoftRAID. The X support- I take it you can see your striped volumes on the X desktop, Greg- is enticing. 'Course softRAID will supposedly have that in a few months plus perhaps they'll beef up other features, maybe including better mode page parameter choices....

02-01-2002, 09:55 PM
So as I read this, OT, is HDT the only set of drivers for our multiple SCSI disk, striped RAIDs, mirrored RAIDs, and partions that can be seen by OSX?

I loose all attached partions (striped and mirrored) under softRAID when booting under OSX.

In other words, how can I see my four disk RAID under OSX?

Make sense?

Any help?



02-01-2002, 10:33 PM

That ones been discussed by a bunch of folks, I'll tell ya! The consensus is that you'll not be able to see a OS9 software raid in OSx and vice-versa, probably ever.

You won't see anything except hardware raids crossing the OS boundries. It would cost a bunch of dough to write code that was duplicated by more code in a totally different operating system. The routines used to access disk are very different in OSX.

The other problem with a cross OS utility is the total lack of a future with OS9, a dead end street with no turn-around. Any investment by a software developer would be a total loss.


02-02-2002, 09:58 AM
Oh OK, I misunderstood Greg's post- it sounded like he sees his FWB -driven stripe on his OSX desktop and can use those disks in X as well as when booted in 9.... http://www.macgurus.com/ubb/confused.gif

02-02-2002, 01:25 PM
I use(d) SoftRAID w/o having mirror or striped volumes. But there are problems even with that in OS X 10.1 so I installed FWB's driver and partitions. (I also used Apple Disk Utility to format and partition but wanted to give HDT a shot at it).

ATTO ExpressStripe 1.0 does support multiple stripped volumes unlike Apple's and right now those volumes cannot be seen in OS 9 (disregarding having OS X server RAID and clients running OS 9). However, ATTO has announced plans to allow using those their StripeRAID volumes in OS 9.

SoftRAID, once it supports OS X, will (or hopes?) to have access in both OS X 10.1+ and OS 9.

I never mentioned having a RAID setup. I have tried Apple's and ATTO's and found problems that may be software, ATTO UL3S firmware, or a bad cable or power cable inside my box. But SoftRAID-X should have an initial product for OS X in 2-3 months.

One 2G X15 maxes out the B&W's bus. I barely get into the X15's performance curve (low end) and hit a wall, maxes out. NO benefit from stripping them. I'd have been better off maybe with one 36GB drive rather than two smaller drives. A warning to B&W owners investing or thinking of trying to get the best performance: you'll need a QS G4.