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01-15-2007, 09:09 AM   #1
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Any PC Networking Gurus here?

Here's my plight. I'm out of disk space. I filled a 200gig drive in 6 months. So, I've decided to install a NAS to my network. The system I'm looking at is an Intel 4 drive NAS. I plan on 4 500 gig drives in a level 5 raid array for a total of 1.5tb of storage.

I know in a level 1 array, if a drive fails I can still use the array in a degraded performance mode until I can replace the failed drive.

In raid 5 I know that in the event of a failed drive, the array gets rebuilt when the drive is replaced.

My question is, can I continue to save to the array in degraded mode, like a raid 1 array, or am I shut down until the failed drive gets replaced?

Any help and advise is appreciated.
-Alan

01-15-2007, 05:08 PM   #2
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yes, thats the advantage of having a RAID (that Mirrors, or RAID 1)

just replace as soon as possible..(happened to me a few times..already, mild panic attack when you come to work, and the server is beeping for no reason what so ever...)
01-15-2007, 05:19 PM   #3
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Hi Alan.
You had me thinking, (thats dangerous BTW) I pulled out my class A certification book and I'm sitting here looking at RAID 5 disk striping with distributed Parity. Unlike a dedicated Data and parity drive (like the RAID 1) RAID 5 distributes the data and parity information evenly across ALL DRIVE. You would need at least 3drives but the storage would be limited to only the size of one drive. Say if you have 3 200gb drives your total storage capacity would be 400gb (not the 600gb You would have in a Raid 1 array.)(If you had 4 200gb drives you would have 600gb storage.)

Now to answer the question about a drive failing. If one drive fails it's portion of the striped data can be re-created from the remaining data and parity bits, as long as only one of the drives fail. In RAID 5 it is rare that more then one drive would fail at a time.

Hope this helped.

Good Shooting.
Cheers: David

PS The information and more can be found in the All In One A+ certification Exam guide fifth edition by Meyers/Jernigan Pages 384-385 and page 429
01-15-2007, 05:29 PM   #4
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QuoteOriginally posted by roscot Quote
Here's my plight. I'm out of disk space. I filled a 200gig drive in 6 months. So, I've decided to install a NAS to my network. The system I'm looking at is an Intel 4 drive NAS. I plan on 4 500 gig drives in a level 5 raid array for a total of 1.5tb of storage.

I know in a level 1 array, if a drive fails I can still use the array in a degraded performance mode until I can replace the failed drive.

In raid 5 I know that in the event of a failed drive, the array gets rebuilt when the drive is replaced.

My question is, can I continue to save to the array in degraded mode, like a raid 1 array, or am I shut down until the failed drive gets replaced?

Any help and advise is appreciated.
-Alan
If you lose a disk in a RAID5 configuration, you can continue to use it for reads and writes in the event of a disk failure. If you lose a 2nd disk in this mode, you will lose *all* of your data, so replace that failed disk as soon as possible. Disks in common lot numbers sometimes have been know to fail around the same time.

In a degraded mode, you will notice that things do not read or write as fast as they did before, with about a 25% drop in performance. That is because the system has to calculate the data from the parity bit for every access. It adds more load to the system.

But, the bottom line is that is still works.

Good luck.

Jeff

01-15-2007, 06:19 PM   #5
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QuoteOriginally posted by Photo Tramp Quote
Hi Alan.
You had me thinking, (thats dangerous BTW) I pulled out my class A certification book and I'm sitting here looking at RAID 5 disk striping with distributed Parity. Unlike a dedicated Data and parity drive (like the RAID 1) RAID 5 distributes the data and parity information evenly across ALL DRIVE. You would need at least 3drives but the storage would be limited to only the size of one drive. Say if you have 3 200gb drives your total storage capacity would be 400gb (not the 600gb You would have in a Raid 1 array.)(If you had 4 200gb drives you would have 600gb storage.)

Now to answer the question about a drive failing. If one drive fails it's portion of the striped data can be re-created from the remaining data and parity bits, as long as only one of the drives fail. In RAID 5 it is rare that more then one drive would fail at a time.

Hope this helped.

Good Shooting.
Cheers: David

PS The information and more can be found in the All In One A+ certification Exam guide fifth edition by Meyers/Jernigan Pages 384-385 and page 429
Unfortunately, this information is not 100% correct (I've taken A+ courses, and I have despaired at the information in some of the books- I've also taken MCSE courses and not been overly impressed with some stuff in there too).

In RAID 5, you are not limited to the capacity of ONE drive. If you have X drives in an array, you have X - 1 drives' worth of capacity. For example, with 3 500GB drives, you will have 1TB worth of capacity. 3 drives (1.5TB), with the equivalent of one (500GB) being used for parity. (Wait... looking back over your explanation, you have it right, but typed "one" instead of "two".)

A little information on some more popular RAID levels:

If your data (in chunks of D1, D2, D3, D4, etc.) and parity (P1, P2, P3, etc.) are written to the arrays, you end up with the following:

RAID 0- data striped across all drives:
Drive 1: D1, D3, D5
Drive 2: D2, D4, D6
Lose one drive, you lose it ALL. This is pure speed, no redundancy or fault-tolerance.

RAID 1- No parity, just mirroring:
Drive 1: D1, D2, D3, D4, D5, D6
Drive 2: D1, D2, D3, D4, D5, D6
Lose one drive, you lose nothing. This is just redundancy, no increase in speed (actually a slight hit).

RAID 4: One drive of the array (3+ drives) is used for mirroring, data striped across the rest:
Drive 1: D1, D3, D5
Drive 2: D2, D4, D6
Drive 3: P1, P2, P3
Lose one drive, you can still survive.

RAID 5: Like RAID 4, but everything is striped:
Drive 1: D1, D3, P3
Drive 2: D2, P2, D5
Drive 3: P1, D4, D6
Again, lose one, and you're still in business. This is more fault tolerant than the others.

Generally, unless you REALLY needed a huge single drive array, I would recommend against RAID 5 for most people. The complexity and cost is rather high; better to invest in a next-gen DVD drive (like Blu-Ray or HD-DVD) or a mega capacity backup solution.

Newegg.com - LITE-ON 2X Blu-ray Disc Triple DVD Burner Black SATA Model LH-2B1S - Retail
01-15-2007, 07:17 PM   #6
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Thanks to all for your responses. You've been very helpful.

Cheers
-Alan
01-15-2007, 07:26 PM   #7
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QuoteOriginally posted by roscot Quote
Here's my plight. I'm out of disk space. I filled a 200gig drive in 6 months. So, I've decided to install a NAS to my network. The system I'm looking at is an Intel 4 drive NAS. I plan on 4 500 gig drives in a level 5 raid array for a total of 1.5tb of storage.

I know in a level 1 array, if a drive fails I can still use the array in a degraded performance mode until I can replace the failed drive.

In raid 5 I know that in the event of a failed drive, the array gets rebuilt when the drive is replaced.

My question is, can I continue to save to the array in degraded mode, like a raid 1 array, or am I shut down until the failed drive gets replaced?

Any help and advise is appreciated.
-Alan

I believe that it mostly depends on which NAS solution you choose (brand name like Buffalo for example)
As far as I know part of the attraction of most NAS systems is the ability to hot swap if one of the drives fails.

randy

01-15-2007, 08:35 PM   #8
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Roscot, just like all the other guys said, if you are using a RAID 5 array and 1 drive fails you can still use it but fix it (replace the failed drive) ASAP. This is because if a second drive goes you're toast. RAID 5 will run on a minimum of 3 drives.

If you are looking into a cheaper solution, you may want to consider building yourself a very cheap (eg. Celeron) "whitebox", then pop one of these cards in it.

Sabrent RAID SATA II – 3Gbps Internal Dual Ports PCI-Express Host Sata Card SATA-PE44 in Canada at TigerDirect.ca

HighPoint RocketRAID 1820A 8-Port SATA RAID 0, 1, 5, 10, JBOB PCI-X 64-Bit Controller (RETAIL BOX) RC-HPT1820A in Canada at TigerDirect.ca

I haven't tried these cards as my experience is with SCSI in a server environment. I don't know the Sabrent brand, but HiPoint has been in the hard drive controller game for a while - I can remember them on ABIT boards designed for Pentium 3's. Just make sure your board is compatible. (PCI-X not the same as PCI-E aka PCI Express)

Two tips. Don't cheap out on the power supply or the case. Get some high quality, quiet fans. A raid array will be quite hot and loud.

Last edited by Alvin; 01-15-2007 at 08:46 PM.
01-15-2007, 08:51 PM   #9
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QuoteOriginally posted by -=JoN=- Quote
happened to me a few times..already, mild panic attack when you come to work, and the server is beeping for no reason what so ever...)
So so true! It works better than a cuppajava. That or the server room is HOT because the a/c has failed. (Servers DO NOT like 40 degree Celcius environs!)
01-15-2007, 11:09 PM   #10
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QuoteOriginally posted by Alvin Quote
So so true! It works better than a cuppajava. That or the server room is HOT because the a/c has failed. (Servers DO NOT like 40 degree Celcius environs!)

heh, true...summer time, my exhaust fans in my server closet goes up to full blast (auto temp sensor) thats in addition to the ac in the office..(sadly not a dedicated room)...

RAID 5 is over kill....not sure if it will be cost effective just for normal documents and photo back ups..(still prefer optical media over hard disk, as hard disks can still and will fail....)

for backing up remember, redundancy is rules all
01-16-2007, 12:12 PM   #11
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Not talking back ups here. This is going to be my main data storage facility. For the time being, I can bacl upto a series of external USB drives I own. At least until I out grow them.
01-16-2007, 12:14 PM   #12
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I was considering building my own, but I'm not a network wiz ( I do DBs) and having a prebuilt web based storage management system is a big plus.
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