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Raid 5 guestions??

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patrickl:

--- Quote from: Samstag on February 01, 2008, 09:33:24 pm ---I went with RAID 5 so I can stop worrying about backups.  It seems silly to use single external drives to backup fault-tolerant arrays.  If you don't feel comfortable with RAID 5, spend a little more for RAID 6.  If you're really worried about more than two drives failing at once, you can add as many redundant drives as you like to the array and not have to worry about filling up slow USB drives.

--- End quote ---
There are several reasons for backups. I move the external drives to a different location. The RAID system will be lost in case of theft or fire. RAID does not protect you there.

Also I have had major disruptions in basically every RAID array I have ever owned. I've had simultaneous drive failures twice. Once the whole array was lost and another time I could repair one drive. I put it in another computer and repaired it with a Seagate toolkit), but it took me a while before I was brave enough to try that. I was afraid it might break the array. I've also had OS failures after Linux upgrades rendering the array inoperative. With the extra backup at least I was able to use the files still.

So the external backup is to protect against physical damage and total array failure. You should never rely on RAID alone.

BTW an important thing is that you get a warning when something starts to fail. That's what I have always been missing in my own built RAID solutions. The first time I had a double drive failure, I simply didn't know one drive was broken until finally two drives failed and the thing stopped working.

Although even on the commercial solution I had a double drive failure. I had set up e-mail warnings on my ReadyNAS, but after I had changed my network settings the raid array was unable to send me an e-mail about the drive failures. Still it has saved me from possibly damaging situations several times already.

Of course you can have a daily check of the logfiles, but who does that? If you are even able to see the errors in a logfile. I've had 2 hardware RAID solutions that did not log errors. One needed a RS232 tool to read the status of the array and another relied on blinking LEDs (on the board ... inside the PC!!!)

patrickl:

--- Quote from: boykster on February 02, 2008, 03:42:23 am ---Its all about abstracting the "system" from the "storage".  I have 3 RAID5 arrays on 2 systems.  Depending on what computer has the RAID cards and drives installed, those arrays could live on any computer.  The OS and the storage arrays are independant. 

--- End quote ---
I realize that you need to keep the OS and the data separate, but I don't think is a separate drive is logically more separated than a separate partition. It's just one digit difference in the mount table.

I've actually had my OS drive fail. That sure took the array down. I guess it was my own fault, because I thought I could get away with using some old drive. But still, any drive can fail.

Actually the ReadyNAS installs the OS on one of the drives too. It's mostly soft RAID afterall. Although if the drive fails it installs it from flash again on another drive. So there shouldn't be downtime if the OS drive fails, but of course if the OS drive fails you never know for sure everything keeps on working.

squirrellydw:

--- Quote from: boykster on February 02, 2008, 03:42:23 am ---
--- Quote from: squirrellydw on February 02, 2008, 03:16:12 am ---OK, I understand raid 5 and 6 pretty well but what does the hotspare do?  I will probably use the adaptec card with a raid 6.

--- End quote ---

A hotspare drive is just a drive "in waiting" in case a failure happens.  If a drive fails in a RAID array, rather than waiting for user intervention to swap out a bad drive, the hot spare is swapped in and hte array is rebuilt.  Its an additional (-1) in the whole scheme of things, and adds an additional level of "safety".


--- End quote ---


Thanks, I like that idea also.  I probably won't start building this for another 3 months but at least I know more now and can really look at and understand what I need.  I won't my data to be as safe as possible.

lcddream:

--- Quote from: patrickl on February 02, 2008, 03:52:13 am ---BTW an important thing is that you get a warning when something starts to fail. That's what I have always been missing in my own built RAID solutions. The first time I had a double drive failure, I simply didn't know one drive was broken until finally two drives failed and the thing stopped working.

Although even on the commercial solution I had a double drive failure. I had set up e-mail warnings on my ReadyNAS, but after I had changed my network settings the raid array was unable to send me an e-mail about the drive failures. Still it has saved me from possibly damaging situations several times already.

Of course you can have a daily check of the logfiles, but who does that? If you are even able to see the errors in a logfile. I've had 2 hardware RAID solutions that did not log errors. One needed a RS232 tool to read the status of the array and another relied on blinking LEDs (on the board ... inside the PC!!!)

--- End quote ---

My 3ware 9550sx will email me with any problem that occurs.

patrickl:

--- Quote from: squirrellydw on February 02, 2008, 11:00:32 am ---
--- Quote from: boykster on February 02, 2008, 03:42:23 am ---
--- Quote from: squirrellydw on February 02, 2008, 03:16:12 am ---OK, I understand raid 5 and 6 pretty well but what does the hotspare do?  I will probably use the adaptec card with a raid 6.

--- End quote ---

A hotspare drive is just a drive "in waiting" in case a failure happens.  If a drive fails in a RAID array, rather than waiting for user intervention to swap out a bad drive, the hot spare is swapped in and hte array is rebuilt.  Its an additional (-1) in the whole scheme of things, and adds an additional level of "safety".


--- End quote ---

Thanks, I like that idea also.  I probably won't start building this for another 3 months but at least I know more now and can really look at and understand what I need.  I won't my data to be as safe as possible.

--- End quote ---
Wouldn't it make more sense to use RAID 6 then?

RAID 6 would use that extra disk for extra protection of the array instead of it sitting idle.

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