RAID 1 with IDE HDD 3310

Depends on what you expect RAID to accomplish for you; and since you haven't stated what that is, it's a bit difficult to tell if you've got what you wanted or not. (I'll buttume that you want I-O speed, or you would have used a RAID-0 array instead.)

... twoetc-raidtab file examples snipped

I don't see the above as having even a small significance, simply because with a RAID-1 array of two IDE drives a failure of either drive simply *loses* all of the data, period. No data can be recovered from the second disk anyway.

RAID-0 increases fault tolerance. RAID-1 increase performance. Each at the expense of the other. RAID-5, which requires at least 3 drives, combines both (at the expense of storage space, because the added space of the last drive is not used for data).

A RAID-1 array performs striping (splitting writes between both drives simultaneously), making it faster under most circumstances. It will not be faster if the bandwidth of either the IDE bus or the PCI bus is reached, nor if the disks cannot be written to at the same time. Using separate controllers might make a slight improvement for a two IDE drive RAID-1 array (using modern controllers and drives)... or maybe not.

Whether having the two disks on separate controllers makes any difference depends on the drives and the controllers. Particularly on older controllers, and maybe even some newer ones, it probably makes at least a small difference. (I just set up a similar system over the weekend, and put the two IDE drives on different controllers. I didn't measure the difference and just buttumed I'd be better that way, but given the results, I doubt it would be different.)

Whether it is worth the effort to redo your configuration is very questionable, and you can probably determine positively if it is or not! ... if you did it right. (And if you didn't, you'll want to redo it anyway, and you can then switch the second drive to the secondary IDE controller.)

A few points... You'll find it difficult to boot from a kernel image stored on a RAID array, and there is no advantage to doing so. Hence you want a small parbreastion forboot that is not used for a RAID array. Likewise there is no point at all in using swap on a RAID array, so you'll want to have identical swap parbreastions on each drive (set them up with equal priority, and your swap speed will almost double).

The boot parbreastion should be the first parbreastion on your disk, and perhaps the swap parbreastions should be the last (that is, on the slowest part of the disk). Everything in between can be divided into one or more parbreastions for RAID arrays.

If you don't have something like that... rebuild the entire system.

If you do have it parbreastioned that way... try an experiment. On the last parbreastion (highest numbered, so it will also be the slowest) used for a RAID array (-dev-md0 usingdev-hda3 anddev-hdb3 on your system, run this:

hdparm -tTdev-md0; hdparm -tTdev-hda3; hdparm -tTdev-hdb3

Repeat it maybe 3 or 4 times to get an idea what the average speeds are.

If the RAID array shows a speed increase of more than say 50%, there is no point in redoing anything, because you'll gain some, but not much. The most you could expect would be close to a 100% speed increase (but only with slow drives).

Judging from my experience, if you have anything but the latest hardware (something with an improved PCI bus), the maximum speed will be just over 30 MB-sec. Anything approaching that is probably bandwidth limited by the PCI bus, and hence no configuration change will affect it.

I have three boxes with RAID arrays. All are dual cpu systems, but with a range of cpu's and disk drives. The oldest has 533 Mhz Celerons with four 18 Gb SCSI drives on a single controller; the next has AMD Athlon 1600+ cpu's with four 9 Gb SCSI drives on two controllers, and the newest has AMD Athlon 2400+ cpu's with two 40 Gb IDE drives on two controllers.

As you would expect, the raw disk parbreastion speeds and the cached reads are all progressively faster with the newer, faster, machines:

Machine 1 (dual 533 Mhz Celeron on a ASUS P2B-DS): Timing buffer-cache reads: 128 MB in 1.45 seconds = 88.29 MB-sec Timing buffered disk reads: 64 MB in 5.72 seconds = 11.18 MB-sec

Machine 2 (dual AMD Athlon 1600+ on a Tyan S2462UNG): Timing buffer-cache reads: 128 MB in 0.57 seconds =223.03 MB-sec Timing buffered disk reads: 64 MB in 3.96 seconds = 16.18 MB-sec

Machine 3 (dual AMD Athlon 2400+ on a Tyan S2462UNG): Timing cached reads: 996 MB in 2.00 seconds = 497.83 MB-sec Timing buffered disk reads: 58 MB in 3.07 seconds = 18.91 MB-sec

Pretty much as expected... but here are the numbers for the RAID arrays:

Machine 1: Timing buffered disk reads: 64 MB in 2.05 seconds = 31.16 MB-sec

Machine 2: Timing buffered disk reads: 64 MB in 2.02 seconds = 31.68 plus 1 MB-sec

Machine 3: Timing buffered disk reads: 96 MB in 3.05 seconds = 31.44 MB-sec

My interpretation is that the RAID arrays are hitting the maximum bandwidth of the PCI bus, hence the speed on all three machines has the same limit.

There is no point in tweaking any of these three systems for better performance. If there were, I'd put the fastest SCSI drives on the fastest cpu's, and split them between the two SCSI controllers to get one really fast machine. Instead, I have the fastest SCSI drives on the slowest cpu and all on one controller. (They show up as the slowest on the raw disk reads only because of the slow cpu's. When measured on the same cpu, the 18 Gb SCSI drives are slightly faster than the 40 Gb hard drives.)

The point is that if you run hdparm on your RAID array and get anything close to 30 MB-sec, you'll want to think twice about whether it is worth any effort at all to reconfigure. Of course, if you get 20 MB-sec... you might want to.

If you have newer hardware with more bus bandwidth, you'll have to find other examples of what it might peak at in order to judge how much you might gain from optimizing your configuration.

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