View Full Version : Raid facts

08-28-2001, 05:38 PM
Hi all, I just wanted to check the facts on raid as I now believe I understand them. I have a new Quicksilver, 867. It came with a 60g ATA100 IBM drive. I installed a ATTO U3DC card for SCSI raid. I acquired another identical ATA 60g drive that isn't installed (I don't know whether or how to benifit from this drive).

Raid Facts as I know them;

1. I can raid0 striped and/or raid1 mirror via the ATTO card with Softraid,FWB etc .

2. I can partition and run a partial stripe and partial mirror on same drives.

3. Running two striped cheetahs on the same channel will give similar performance as running them on separate channels.

4. Placing pairs of cheetahs striped on both channels will give better performance yet. The problem with this is the added costs of external enclosures.

5.Use of multiple 'lesser' speed drives than 15k cheetahs may give better performance than just 2 top of the line cheetahs.

6* There is no performance to be gained setting up RAID0 with software on ATA.(?)

7. There is no way to raid with the motherboard ATA bus.

8. The only PCI Raid ATA host cards are ATA66 cards, no ATA100 cards availiable for macs.

9. Hardware raid cards can generate significant read write performance gains for ATA drives.

10* There is no way currently to raid1 mirror ATA drives on the mac.(?)

I have a question as to whether ANY performance gain would be seen useing a Raid ATA66 host card and the two IBM ATA100 drives. With the factory drive the sustained read via ATTO bench was 61.70, the sus write was 58.28 on the factory bus. That's better than any of the results I have read useing raid host cards and for instance 10K Maxtor drives. I believe we will soon see ATA100 raid host cards hit the market, they have for PCs, that might improve the perfomance.

As SCSI3 drives mature, I will set up a Striped Raid with Cheetahs on the ATTO U3D host card for speed, at this time I cannot afford to make the drive purchase so am useing older cheetahs. I need a Raid1 mirror for some of the data files that I can't loose. I currently do frequent CD-RW backups of some of those files, I would prefer the added security of the mirrored volumns. Is there any way to use partitions of the ATA drives in mirrored raid? The drives are sitting on my bench, idle.

Am I wrong about raid performance with hardware host cards and ATA100 drives. Would I see significant performance gains with them in raid0? If so, I could then dedicate some of the cheetah space to mirroring.

Please feel free to correct and expand on my above list. I have only looked into the RAID technologies recently and have a lot to learn yet. I don't want to duplicate everyone elses knowledge base.


[This message has been edited by ricks (edited 28 August 2001).]

09-02-2001, 12:39 PM

1) Yes

2) Yes - as far as I know. I've never tried this, but I've heard it works and from running softRAID - it seems feasable.

3) Yes - assuming that the two stripped Cheetahs (or any other drive) does not exceed the bandwidth of the channel. Of course with 160MB/s per channel you should be safe for a few years, then new drives will come out http://macgurus.com/infopop/emoticons/icon_wink.gif

4) Yes - you can stripe across channels or run separate RAIDs one each channel. Of course at this point your PCI bus may be the limit http://macgurus.com/infopop/emoticons/icon_smile.gif I have never stripped across channels as I dont have the money for an U160 Dual Channel - yet. The added cost is mainly in the cabling. You only need ONE external box - or a case that can handle that may drives internally.

5) Well from what I've read a single X15 Cheetah is equal to 2 or 3 10K Cheetahs - so you may even save money getting one or two 15K drives vs. 2 to 4 10K drives. Also Seagate now has a 36GB Cheetah. Remember everytime you add a drive - you increase the chances of failure. Sure top of the line SCSI is very trouble free, but there is still a failure rate and MTBF. I would guess the practicle RAID-0 limit would be 8 drives or less... on a Mac.

6) I think you do gain a little bit with a software RAID-0 speed with software on ATA - but its not much.

7) Correct - unless 10.1 will support it now http://macgurus.com/infopop/emoticons/icon_smile.gif

8) Yes I think this is correct, but SCSI is still faster and more expensive! http://macgurus.com/infopop/emoticons/icon_biggrin.gif

9) Yes, again I think this is correct - even with a hardware ATA/IDE RAID - raid-1 (mirrors) are not practical.

I've heard that an ATA/100 card is in the works (or even available - from Sonnet?) and that it would be flashable up to ATA/133 standards. This sounds like a nice card. It should be supported in X too - since several ATA cards are already working fine with X.

OK - SCSI- 3 is very vague. I think you mean ULTRA3 (or Ultra160 - a 'subset' of U3). It is important to keep the terms correct - as it can get very confusing very quickly otherwise http://macgurus.com/infopop/emoticons/icon_smile.gif Is there any way to use partitions of the ATA drives in mirrored raid? The drives are sitting on my bench, idle.
Not that I know of - you will need to use the ATTO SCSI card with SCSI drives. The whole point of a mirror is for added security & reliability of the data. Using anything less than Gurus style SCSI will compromise this and render your quest for monentary efficieny moot. http://macgurus.com/infopop/emoticons/icon_smile.gif

That would probably work well - using the IDE/ATA for RAID-0 (speed) and the SCSI for RAID-1 (mirroring). From what I know you can not boot off a RAID-0 on a new mac. You may be able to boot off a mirror - although I've heard it can have issues. You can only get about 4 HDs in a sawtooth style case, so you will hit that limit soon.

I'm sure others will add what I left out...

Life in the fast lane leads to:
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09-04-2001, 02:33 AM

I just saw Kayes posting on the 'single v dual' Raid posting. WOW. I had no idea such performance was availiable via the 2nd gen X15s. I can taste it, wish I could afford it. (not until spring when business kicks up again)

Read on XLR8's site some interesting numbers for hardraid with Sonnets ATA66 raid card and IBM 75GXP drives. High 90s for sustained R/W. Also Acard has announced their new ATA100+ Raid card is out, delivery in mid sept. They are claiming 'double' rates with raid0 and full compatability with Booting OS9 and OSX. Sonnet will prob sell this with their name on it if they follow their history.

Your suggestion that I use the ATAs for raid0 and some of the SCSI for mirroring is probably what I'll end up doing. I won't boot from the mirror so that shouldn't be an issue, just keep the data files on it.

I almost gotta see what the ATA100+ raid card will do with 60GXP ATA drives.The cost for the whole shebang would be around 500 bucks.(2 60g drives+card and I already have the drives) That's what I paid for the UL3D Atto card alone, darn near. NO way to get the performance of the SCSI raid, that's for sure though.

Thanks for the feedback, I'll be usein' it.