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Installing RAID


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#1
Grantax

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This is what I've done: (With 2 formatted hard drives)

1. Enabled RAID for Serial-ATA 1 and 2. (That's where I have my 2 harddrives)
2. Restarted the computer.
3. Pressed F10, to configure RAID.
4. Chose mirroring and added both harddrives. (There's a "Boot" option I had there, which I left at default, which was NO, because I don't know what it means)
5. Inserted the Windows XP Cd, and started it.
6. Pressed F6. (To install 'Third Party SCSI or RAID drivers' or something like that)
7. Inserted the Raid floopy disk, and installed what was on it.
8. Installed Windows.

But a friend said that raid wasn't installed yet.. is it?

(I should have 2x read speed now, but it looks like I have 0.2x read speed, because when I didn't use raid, the computer loaded windows in about 4 seconds, now it takes 10 seconds... Less crap installed in windows, raid, it doesn't make sence that it takes 2.5x the time to load windows now.)

Edited by Grantax, 25 February 2006 - 07:46 AM.

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#2
Kemasa

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It sounds like the RAID setup should be installed if you configured it.

I think you don't know exactly how things work with RAID since you have an unrealistic expectation that it will be twice as fast. In reality, some RAID setups can be slower. In the case of RAID1, the write has to occur with both disks and unless the read access can read from both disks, it will not be faster.

The main reason for RAIDis for data protection, not speed, unless you get into the higher end systems (not PCs).
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#3
Grantax

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I know it's for security.
But I thought it would also get 2x read speed because it could read from both hard drives..

Thank you for your answer
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#4
Kemasa

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In some cases it can improve read speeds, but it is not always the case. There is also overhead associated with it and there are limits to the data transfer within the machine.

If you are reading short files, unless you know that there are two possible sources for it, you won't know to get files from each source, also unless you have a list of the next file to read, you won't know to go get it before you need it.
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#5
Neil Jones

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I know it's for security.
But I thought it would also get 2x read speed because it could read from both hard drives..


It doesn't read from both hard drives all the time, it depends how the filesystem has arranged the files.

You'll only usually see the benefits of RAID if you've set it up as a RAID 0 array, this is the faster one but at the expense of no data backup if one of the drives fails.

Even then, the RAID only uses both drives if it has to; if a file has been spread in such a way so as to end up split across the two disks. If it should so happen that a file exists purely on one of the drives, the other one won't be spinning.

It's a common misconception that you see twice as fast speeds on a RAID regardless, because this isn't always the case depending on how the files have ended up.
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#6
Kemasa

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It doesn't read from both hard drives all the time, it depends how the filesystem has arranged the files.

You'll only usually see the benefits of RAID if you've set it up as a RAID 0 array, this is the faster one but at the expense of no data backup if one of the drives fails.

Even then, the RAID only uses both drives if it has to; if a file has been spread in such a way so as to end up split across the two disks. If it should so happen that a file exists purely on one of the drives, the other one won't be spinning.


Sorry, but what you are saying is not true. In the case of RAID1, mirrored disks, it can read the data from either drive and if the software/firmware is "smart" enough, it will read from both disks in order to speed things up. Even individual disks can order the operations to perform better rather in order of the requests.

RAID0 (AID really) is no faster than a single disk, all it means is that the data is spread over two or more disks instead of one. There is no speed increase possible unless the data is on two different disks.

Sigh ... It is ALWAYS the case that ALL the disks are spinning in a RAID array. Writes occur across several disks, as well as data checks. In the case of RAID1, both disks have to write the data and keep in sync. I have no idea of why you would think that one of the disks would not be spinning. If it was not in operation, then it is usless and not a RAID array at all.

If you were to do a backup to disk, then the backup could not be running unless you needed it, but that is a completely different story.
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