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Raid 0 total space calculation

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August 31, 2011 12:17:58 PM

aloha
I am a bit confused.
I am sure I have seen posts online and even been told that raid 0 adds up all the drives to get your total space and that makes sense to me because you are choosing which drive to write to based on faster performance not writing to every drive which would be a different raid level.

now I am messing around with setting up a simple raid using a ram disk just to play with it and when i choose striped volume and add 4 1gb disks together I get a 1gb disk.

so is striped not the raid 0 or what?
a c 279 G Storage
August 31, 2011 12:56:37 PM

Where are you doing the striping? In Disk Manager? In what version of Windows?

A few points for clarification. First, RAID 0 isn't really RAID, since the "R" stands for "Redundant" and there is no redundancy in RAID 0. (Oddly, the I stood for Inexpensive when RAID was invented, and now stands for Independent.)

Second, RAID 0 does not choose which drive to write to based on faster performance. It writes one stripe-size worth of data to disk one, the next strip-size to disk two, and so-on in round-robin order. Again oddly, this does increase the transfer rate but may cause slowness with double seeks.

As a total aside, there are striping mechanisms that get around the seek issue and the stripe issue, where disks spin in perfect sync and striping is one-byte-per-disk or even one-bit-per-disk. This has advantages: for small reads you are still using all disks, and there is only one seek time.

===================================

Clarifications done, what you describe of striping four 1 GB drives and getting 1 GB result sounds more like they went into RAID 1, mirroring. That's why I asked for more detail on the process you used to stripe them together. A snapshot of the configuration (of the BIOS if you did it in BIOS, the Disk Manager if that's where you did it) would help us to see what is happening.

September 1, 2011 3:20:51 AM

aloha
sorry I forgot to post back.
it was a bit confusing
it asked me what size drive i wanted and gave me the option for up to 1gb
but when i choose that size then the actual drive size reported in explorer was 4gb.

please tell me more about the striping mechanisms that can improve the small reads performance.

I have some physical drives arriving today that i want to put into raid over the weekend.

by the way you are the first one I have seen to actually explain why raid 0 is not raid.

that particular raid is raid vs not raid has many threads you can find online.

however since it does not have another name I guess i will keep calling it raid until they decide to rename it.

Related resources
a c 279 G Storage
September 1, 2011 1:01:00 PM

A few disorganized thoughts, since I don't have time to make this clean an coherent.

I already told you everything that I know about "striping mechanisms that can improve the small reads performance." I just know that they exist. I would assume that you need specially-built drives to synchronize the spindles, but I don't know. If I wanted to improve small random reads, I would buy an SSD. The best thing that you can do with an HDD-based stripe set is to make the stripe size small, which will make large IOs less efficient.

If I read your post correctly, you see a 4 GB volume so the missing space is no longer an issue.

I have found several references to synchronized spindles but nothing yet on how to do it. One of the best is at http://www.staff.uni-mainz.de/neuffer/scsi/what_is_raid... .
September 1, 2011 3:12:03 PM

aloha
thanks for that info
I have someone doing some research on the things you mentioned.
If he finds anything out I will post back here the results.
September 8, 2011 3:45:54 AM

hmm I never got any info on that synchronized spindles.

but if you need a special hard drive for it then its probably not what I am looking for.
September 15, 2011 4:17:20 AM

Aloha
so I did set up the raid and its quite speedy.

I was wondering
I moved the computer and two of the sata cables came out
not sure which is which out of the three disks

will that break the raid if I hook up to wrong disk?
the computer was off.

also hypothetically if I was to have unplugged one by accident when the raid was on would I lose all my data or would I just lose a bit of data that was currently being written / read when the cable came out. of course I mean if I shut down and plug it back in or just plug it in right away will I lose all the data?

thanks
September 16, 2011 6:07:23 PM

Well I guess i am going to find out myself
!