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thor
10-20-2000, 07:27 PM
Can someone explain the optimum settings in SoftRAID 2.2.2 in the Drive Mode Parameters? Info on these settings seems a bit hard to find, even on SoftRAID's site.
I am interested in what the buffer full/empty ratio should be set at, and the # cache segments? When I installed my 2-9 gig cheetahs on the Miles U2W card, and initialized them with SoftRAID, the default of the #cache segments was set to 16. After changing this to a lower number (my other 3 barracuda drives on the internal SCSI bus are all set to 1 cache segment), I can no longer set it back to 16. It seems 10 is the highest #cache segments it will allow me to type in now...what gives? More importantly whats does it all mean?

thanks for any insite you have

magician
10-20-2000, 09:17 PM
I just leave that stuff at defaults.

I think K messes around with them, though. He'll probably be thru here in a bit.

To reset your drivers to defaults, you may need to update drivers, or even reinitialize. Only Mark James would know why it did what you describe, I suspect.

MacMikester
10-20-2000, 10:50 PM
Most of us have played around with these settings after aquiring our Cheetahs, SoftRaid and SCSI hosts. Bottom line is that unless you are doing exactly the same thing with your computer all the time, opening exactly the same size files, transferring exactly the same size files, etc., you cannot optimize these very fine adjustments realistically. It's an empirical science of trial and error. Either you use an artificial benchmark like ATTO ExpressTools or HDT to find the optimum settings or you do exactly what your computer will be doing over and over again and find the optimum performance. Most of us users have such random patterns of file access (big, small, many, few) that we can do neither test properly. In general, if you work exclusively with large file sizes, one at a time, fewer cache segments will be better.

I think 16 is a kind of default number that SoftRaid shows when it isn't controlling the number of cache segments. Maybe it truly is the default setting for Seagate drives but nevertheless, SoftRaid won't set any higher values than 10. Cache segments act like independent caches such that the data prefetched along with the data you need is stored in that segment. If you have 4 segments, you can keep the data in cache from three prior operations while you work on the fourth. The tradeoff is that, if you have a 4 MB cache total, each segment will only hold 1 MB of data. I use 4 segments, YMMV. If you're working with 40 MB Photoshop files all the time, probably one segment is better.

The full/empty ratios are set on a scale of 0 to 256, determining how full or empty the write or read cache will be before the drive begins to write to disk or request data to store in cache. Changing these ratios has little effect in my testing. I leave the settings at half for both (128).

kaye
10-21-2000, 12:26 AM
thor,

SoftRAID does not allow more than 10 cache segments. That said I use 9 cache segments for my three 9GB Cheetahs (ST39204LW) and zero and zero for the full/empty ratios. If you wish to get back to 16 cache segments or something greater than 10, then you need to use something like FWB Configure on Mode Page Parameters page 8. The Cheetah X15 ships with 20 cache segments, and I set 23 and zeroes for full/empty.

One thing to keep in mind is that there are other things stored in the onboard disk cache, such as Mode Page Parameters. So the disk cache is never totally available for use as disk cache. Seagate does not publish how much of this disk cache is used, IBM does. For instance my Ultrastar 9LZX with 4MB cache uses 384KB as I recall. k

kaye
10-21-2000, 01:18 PM
I looked it up and my 9LZX, for example, uses 416KB of the total 4096KB/4MB disk cache. So if you set 4 cache segments, each segment would have 920KB available.

Pretty good explanation here http://www.storage.ibm.com/hardsoft/diskdrdl/library/whitepap/buffer/buffer.htm k

thor
10-21-2000, 08:35 PM
Excellent article,
thank you kaye for the info.
:-)

magician
10-21-2000, 10:11 PM
wonderful thread, gentlemen.

a masterful display of expertise!

PENDRAGON18
11-12-2000, 03:39 PM
So if you have a single drive with 4MB of cache and stripe 4 of these together - you now have 16MB of cache. Assuming this is ALL available for data and you have 8 segments - each segment would be 2MB, right?

Would this work the same if they were mirrored?

thanks,

------------------
Have fun storming the castle!

MacMikester
11-12-2000, 04:42 PM
Hey PD18,

Only the disk data is striped. The caches function completely independently for each drive. You set the number of cache segments independently for each drive. You could set 2 segments per drive and have a total of 8 independent cache cache segments, each a little smaller than 2 MB.

Mas
12-23-2000, 03:38 PM
I have 3 of Quantum Atlas 10KII 36Gb LVD (QM336400TY-LW).
I'd like to find out number of its default(factory configured) cache segment.
Or if anyone know the better number of segment for this drive. I work with graphic, video and 3D, verious size of files but mainly 30 - 200Mb up to 600Mb.

In SoftRAID's mode parameter, I'm testing segment size from 1 to 10. First seg number was 27. As we know, SoftRAID does not support more than seg 10. FWB Configure(HDT version 4) allows us to change to 16, I heard. But Page 8(caching) Edit Mode Parameter in FWB Configure, I don see any choice to change cache segment.
It only show 3 check box,

Write Cache Enable, Multiplication Factor and Read Cache Disable.

Then
Demand Read Retension Priority: 0 (Fixed to its number)
Write Retention Priority: 0 (Fixed)
Disable Prefetch Transfer Len: 65535 (configurable)
Minimum Prefetch: 0 (configurable)
Maximum Prefetch:65535 (Fixed)
Maximum Prefetch Cailing:65535 (Fixed)
This is it!

I tried Restore Factory Mode Page Defaults, Optimize in Edit Mode Page(Is it fine tuning?) and did Default in Page 8 caching and saved. No success. SoftRAID doesn't recognize it.

Many thanks

MacMikester
12-27-2000, 01:15 AM
Ola Mas,

The optimal number of segments would theoretically depend on the size of your total cache and I do not know that for your drives. It is not the same to make 4 segments of a 1 MB cache as it is to make four segments of a 4 MB cache. Regardless of all the speculation about the exact number, it makes sense to think about it logically. First, you want the largest cache possible for any given open task. If you have a lot of tasks (repetitive read/write operations on a given file) open at once, you will get better performance out of more cache segments but these will, of course, be smaller segments. If you are usually working on one or two large files at a time, fewer cache segments will give better performance. It seems logical to have one read cache segment and one write cache segment available for large active PhotoShop files. If you are working with or between two such files, I would use four cache segments. Also, make sure you take advantage of all the PhotoShop file acceleration tweaks that are available in the SoftRaid driver.

Regards