Could a bad harddrive in RAID 1 slow down the other?

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MisterCheif
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Could a bad harddrive in RAID 1 slow down the other?

Postby MisterCheif » Tue Aug 07, 2012 8:29 pm UTC

So my parents computer has been pretty slow for the past several months, which I believed was largely due to not reformatting or anything since we got it 5-6 years ago. Now, since I'm the only person in the house with enough technology experience to reformat it and upgrade to Windows 7 and I'm leaving for college on Monday, we had to hurry up and replace the disc drive that had died a couple of weeks ago so I could upgrade them to Windows 7.

So today we just got a blueray drive (to be swapped into the new computer I plan on building for them during my Christmas break), and I installed it. I must have accidentally loosened one of the cables on the RAID 1 hard drives when I installed the drive, as one of the drives no longer showed up. However, the computer booted probably about twice as fast as before and ran faster. It returned to its old speed when I reconnected the power wire I had accidentally loosened.

So is it possible that one of the hard drives is going bad, and is slowing down the computer (in addition to the need for a reformat - I still plan on doing that as soon as my dad backs up his documents.) Would it be better to disconnect that drive in favor of speed, at the loss of security in case of a crash? (Though be its seemingly large impact on performance, I'd think the one slowing it down will be the first to go.)
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lulzfish wrote:Exactly. Playing God is a good, old-fashioned American tradition. And you wouldn't want to ruin tradition. Unless you hate America. And that would make you a Communist.

LikwidCirkel
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Re: Could a bad harddrive in RAID 1 slow down the other?

Postby LikwidCirkel » Wed Aug 08, 2012 4:37 pm UTC

As far as I know, disconnecting a drive from a RAID should almost never speed up the system. With RAID 1, in theory at least, reads should take 0.5x time and writes should take about the same time when compared to a single drive.

If one drive is behaving slow, it's possible, but I think that's pretty unlikely. If the drive you disconnected failed completely, you might see this if the RAID controller kept re-trying without giving up.

It sounds to me like something is wrong with your RAID setup though, e.g. software and hardware is not configured right.
Try disconnecting the OTHER drive, and see if you still see the speed improvement.

If you still see a speed improvement, something is very wrong.

What kind of RAID is it? Options are hardware, software, or hardware-assisted "fake raid"? (fake raid is by far the most common on consumer systems).
Are there any settings you can change? Does it do something crazy like read everything 2x and compare for mismatches? This isn't commonly done, but data-integrity-paranoid applications would make use of such a feature.

Are you trying to use fake raid without the hardware support enabled? That could cause something like what you see - e.g. in the BIOS, your RAID controller might be configured in independent mode, and the software fake-raid driver can't detect this, and goes on and does it's RAID thing anyway without hardware-optimizations.

MisterCheif
Posts: 253
Joined: Tue Apr 14, 2009 1:24 am UTC

Re: Could a bad harddrive in RAID 1 slow down the other?

Postby MisterCheif » Wed Aug 08, 2012 10:32 pm UTC

LikwidCirkel wrote:As far as I know, disconnecting a drive from a RAID should almost never speed up the system. With RAID 1, in theory at least, reads should take 0.5x time and writes should take about the same time when compared to a single drive.

If one drive is behaving slow, it's possible, but I think that's pretty unlikely. If the drive you disconnected failed completely, you might see this if the RAID controller kept re-trying without giving up.

It sounds to me like something is wrong with your RAID setup though, e.g. software and hardware is not configured right.
Try disconnecting the OTHER drive, and see if you still see the speed improvement.

If you still see a speed improvement, something is very wrong.

What kind of RAID is it? Options are hardware, software, or hardware-assisted "fake raid"? (fake raid is by far the most common on consumer systems).
Are there any settings you can change? Does it do something crazy like read everything 2x and compare for mismatches? This isn't commonly done, but data-integrity-paranoid applications would make use of such a feature.

Are you trying to use fake raid without the hardware support enabled? That could cause something like what you see - e.g. in the BIOS, your RAID controller might be configured in independent mode, and the software fake-raid driver can't detect this, and goes on and does it's RAID thing anyway without hardware-optimizations.


I'm not actually sure, as this is a prebuilt we got from dell years ago. I think it is configured correctly in the BIOS, as it displays it lists the two drives as a RAID 1 array.

It may be that the software is reading everything twice to compare, as my identical (except for the graphics card) computer downstairs has not had performance problems since I reformatted because of a virus, and I didn't reinstall that software. The fact that one drive was disconnected may have prevented it from checking. Once somebody else isn't on the computer I'll check to see what happens when I disconnect the other drive instead.
I can haz people?
lulzfish wrote:Exactly. Playing God is a good, old-fashioned American tradition. And you wouldn't want to ruin tradition. Unless you hate America. And that would make you a Communist.

jdelaporte
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Re: Could a bad harddrive in RAID 1 slow down the other?

Postby jdelaporte » Thu Oct 04, 2012 7:07 pm UTC

It seems your question in your post was whether the RAID drive was slowing down the boot of the machine. I had a similar thing happen, and it was because when I unplugged/replugged all my harddrives the BIOS was looking in the wrong order for the hard disk with a boot sector, starting with a terabyte drive that had no boot sector. It was fixed when I put my boot disk at the top of the list. Maybe check the BIOS advanced settings for hard disk boot sequence.


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