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Thread: Booting From RAID

  1. #1
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    Now that I have a RAID 0 volume and other volumes formatted with SoftRaid, I'm having the previously reported problem of having to use System Picker to change boot volumes. All the SoftRaid driven volumes appear highlighted in the Startup Disk Control Panel.

    Now I discover that the RAID volume freezes on bootup as soon as the backside cache is activated. The only way that I can boot is by checking "Write Through" in the XLR8 Control Panel. Never needed that before. What's happening?

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    I haven't encountered that problem, Louie. Let's see what K says.

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    oh, yeah.

    I spoke to Mark James about that bug, and he indicated that it would be fixed in MacOS 9.1, aka Fortissimo.

    I believe this is now slated for release around Jan, probably MacWorld.

  4. #4
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    Louie,
    exactly the same symptomes I have.
    Although system picker and "write through" are working perfectly for me and also I don't see any noticable speed penalty not using the write-back option.
    Cheers

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    Darin encountered this issue as well. I really haven't since I have pulled all my drives off the internal bus.

    Happend on my brother's 9600 (boy do I miss it) when I reinstalled the 4Gb. Just pulled the system folder off the drive. The drive just authorize all the audio program since they require a drive at SCSI 0.

    j.

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    I think Kaye is off on something directed by the House Goddess. He now has to use System Picker since he switched to 9.04. He does not have to use Write-Through.

    Can anyone explain "Write-Through"?

    It doesn't slow the ATTO results. I'm still getting 76 SR and 70 SW.

    [This message has been edited by Louie (edited 16 November 2000).]

  7. #7
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    there are white papers on the XLR8 site that explain cache flushing and the "write-thru" option.

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    I'm here. House Goddess has released me for a few minutes though my email this morning had several people asking about Gurus questions.

    As soon as I started using OS9.0.4 the Startup Disk CP started showing the problem you descrbe with System Picker the solution. If I boot off of 7.6.1 or 8.6, the Startup Disk CP works fine. Any OS9.0.4, whether on RAID or not, whether on Miles2 or not, even on my original 50-pin HD on the internal chain which has the latest Apple driver and not SoftRAID, has the same problem with the Startup Disk CP.

    Write-Through description from Breedon's site for the xlr8 G3/500:

    "The Advanced settings page will allow you to set the backside cache speed to manual (you select a speed) or automatic (the default based on the card type and bootup testing). At cache speeds above 250MHz, the new 'write-through' cache setting becomes enabled as a safety precaution, since the faster copy-back (default mode) may not be reliable. In both the Genesis and 9600/350, I was able to uncheck this and run copy-back mode at cache speeds of 262.9 MHz (when testing at CPU speeds of 525.8MHz (525.8/262/9/52.6). Results in a different Mac with another sample may not be reliable at these speeds however."

    "Copy-Back (default) vs Write-Through Cache Modes: The default 'copy-back' cache mode is faster as writes are written to the backside cache (and later copied back to RAM if data has been changed). Write-through mode means that each CPU write is written directly to much slower main system RAM. Interesting is that the B&W G3s are set for write-through modes, but with their faster 100MHz memory bus speeds it's less of a performance issue than with older macs with much slower memory bus speeds. The 'Write-Through' option only becomes visible at cache speeds of over 250MHz (i.e. - when running at CPU speeds of over 500MHz)."

    "Although I do not recommended it to others, I was able to uncheck Write-Through mode and still run reliably at the maximum speed this CPU card in these systems would run - 525.8/262.9/52.6. I saw no errors in extensive tests at this speed, but these results may not be repeatable and are not recommended to others."

    "Speculative Processing:
    There is also an option to enable or disable (default) Speculative Processing of the G3 CPU. Speculative Processing is often called 'branch prediction' - where the CPU tries to predict the execution paths of the program code. As noted previously, older Macs do not have 'G3-Clean' ROMs so it is advised to keep Speculative Processing disabled (required for software like Retrospect Backup to work 100% reliably). There is a small (4% or so) performance hit in many applications with Spec. Processing disabled, but Photoshop 5 tests actually showed higher filter performance with it disabled in my tests."

    Now, what does Write-Through enabled do to my PTP with xlr8 G3/500 running 540/270 in OS9.0.4? I ran tests both ways in rebooting after each in MB5:

    No/YesW-T----Proc---FP---Graphics---PubGraphics----Disk/PubDisk
    -noW-T-------1785--2289----3912-------2713-----------yes or no, no change
    yesW-T-------1658--2119----3677-------2645-----------yes or no, no change
    yesW-Tchange-(-7%)-(-7%)---(-6%)------(-2.5%)

    Disk and Pub Disk have to go thru main memory anyway, so I would not expect a change. But Processor, FPU, and graphics go thru the Processor for crunching so they are affected by the main memory of Write-Through. I also tested Memory Throughput with Gauge Pro. No change with Write-Through. It is just the use of main memory with Write-Through that causes the slowdown of certain operations.

    Have I left anything out? k

  9. #9
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    hmmm...i just surfed thru the XLR8 site and couldn't find shineola about "write-thru" mode.

    I'll check with Darin....and look around on my machine. I have a bunch of white papers they have sent me over the years....they just aren't filed as neatly as you would think.

  10. #10
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    The discussion of Write-Through mode I found below was within his review of the xlr8 G3/500 on the software controls page. k

  11. #11
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    OK. Thanks Kaye. Now I know what it is.

    Does your machine default to Write-Through since your backside cache speed is over 250? Obviously it will run either way.

    The question is; why does my machine suddenly need Write-Through to boot with backside cache enabled after switching to SoftRAID and striping two drives? (It will boot with the cache disabled.) My backside cache speed is 240, as it was before.

  12. #12
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    My machine does not default to Write-Through, it defaults to showing the Write-Through check box above a backside cache of 250. It will default to Write-Through if at the beginning of bootup it does that test with the thermometer bar, or if after bootup and at the desktop it opens the control panel and asks if I want to run a slightly faster speed. Otherwise, normal boot at 540/270 Write-Through stays disabled. If I boot with the card's switches set for 500/250, the Write-Through check box is not there.

    "The question is; why does my machine suddenly need Write-Through to boot with backside cache enabled after switching to SoftRAID and striping two drives? (It will boot with the cache disabled.) My backside cache speed is 240, as it was before."

    The info from Breedon's site was from his test of the xlr8 G3/500 card. My guess is that your card, xlr8 G3466 card?, will cause the control panel's Write-Through check box to show anytime you overclock, or any xlr8 card is overclocked. Now to your RAID. Striped RAID really stresses the whole system and I'm guessing that the backside cache just can't handle it.

    As I mentioned in my email, you might be better backing off the overclock rather than accepting the percentage hit I showed for certain MB5 operations. A 7% hit on my card if running 536/268 with Write-Through enabled is the equivalent of going back to 500/250 with Write-Through disabled. k

  13. #13
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    That all makes sense. I wish Darin would jump in here and tell us the straight skinny from the Wizards in GA.

    One thing Kaye; my "Write-Through" check box doesn't appear unless it's been checked earlier. I had to click on "Advanced" with the OPT key held down in order for it to show the first time.

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    Well that blows my theory about Write-Through check box appearing anytime an xlr8 card is overclocked on backside cache. As you said in your email, it must be backside cache above 250. k

    [This message has been edited by kaye (edited 17 November 2000).]

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    Here's really weird one. I backed it off to 466/233/46.6 and it still freezes as soon as the cache is enabled unless "Write-Through" is checked. The slower speed dropped my memory performance about 5%. So, I'm back to 480/240/48 with
    "Write-Through" enabled.

  16. #16
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    Louie,

    Looks to me like Write-Through is the only way to go then. Something about the dual-bus striped RAID the xlr8 card does not like even at stock speeds. Say, I wonder if balance is afflicting you. Pull the power plug on the 9GB 10k Cheetah which is on one of the Miles2 with the X15, whereas the other Miles2 only has an X15, right? You can leave the SCSI cable connected.

    If you boot from one of your non-Miles2 drives, everything is OK at 480/240 without Write-Through needing to be enabled? k

    [This message has been edited by kaye (edited 17 November 2000).]

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    it would be better to pull the SCSI cable and leave the power cable attached.

    I suspect Cooksie may be the only guy who can definitively answer this, but I'm suspecting that your machine is testing cache on start-up, and deciding to enable write-thru at that time. Much of the functionality of the MAChSpeed Control control panel application is automated, and it may be detecting some condition during boot that automatically enables write-thru. This is just speculation on my part. I'll email the cowboys at XLR8 and see if they can jump in here.

  18. #18
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    I have no knowledge about the differences between the XLR8 drivers and for instance the Newertech drivers. Fact is that both drivers have the "write thru" option and on my machine the problem disappears with using the XLR8 driver as well as the Newertechdriver with write thru enabled.

  19. #19
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    No Magician; there's nothing "automatic" about this. From the very first time trying to boot from the RAID it would lock up as soon as XLR8 extension loaded and activated the backside cache.

    Out of desperation (and reading ton's earlier posts), I forced the Write-Through option to appear by Option Clicking the Advanced tab in the XLR8 Control Panel. It never shows unless it has already activated or forced to show.

    Once last night I got it to run without write-through by lowering the backside cache speed below 200. However, the CPU is rated 466/233 and it still needs write-though at that speed.

  20. #20
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    Write-through is a slower, safer method of using the backside cache. Whenever anything is written to the cache it is automatically "written through" to main memory. This causes a slow down of about 10% in general but can also increase stability, especially with PCI cards installed.

    Here are the rules for when write-through is automatically enabled:
    1) When any processor is running faster than 510 MHz
    2) When a G4 is installed on any machine prior to a Beige G3 (from the "clone" era)

    Here are the conditions which will cause the write-through check-box to be visible:
    1) Option-key transition to the Advanced Panel
    2) Write-through already enabled
    3) When any processor is running faster than 510 MHz
    4) When a G4 is installed

    Note that the write through box is always visible when a G4 is installed. The G4 being a new processor at the time of the last build, we felt it would be safer to leave that option available even on newer machines "just in case".

    Hope this helps.

    Chris Cooksey
    Director of Engineering, XLR8, Inc.

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