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disaventage to RAID 5?

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Posted · Original PosterOP

(Asking for a friend) he have 5  2tb 7500rpm hard drives and think about running is raid 5. Right now he is just running them normally and separately. Is there any disadvantage to raid 5?

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Aside from needing to dedicate a minimum of 3 hard drives to RAID 5 and not getting to utilize their full storage capacities, there isn't a huge downside. You'll have slightly more secure data in case something catastrophic happens to one drive, but you are then committed to always having to buy a spare drive to get your system back up and running should one of your RAID drives fail.

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There are a few disadvantages, mostly the Write part. It also doesn't have any advantage on Read part. If 2 disk failed simultaneously, your data is doomed.

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RAID 5 gets more dangerous the larger the drives are. If you ever need to rebuild with 10+TB drives the amount of times it takes under high disk activity is so high that another drive could easily fail. If another drive fails while rebuilding your RAID is lost.

There are better ways to mitigate downtime, build huge capacity and duplicate your data.

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Unless your friend needs (or just really wants) continuous operation even if a drive dies, I do not recommend using RAID of any kind. The only purposes it serves is, as mentioned, ensures continuous operation if a drive fails and combines all the drives into a single volume.


The disadvantages include loss of data on all drives if a second drive dies before the first dead drive hasn't been rebuilt yet (a very real possibility), increased cost, and more difficulty making and maintaining backups. A single volume may seem convenient but it would come at a price for more complication and increased risk for data loss if two drives are dead at any one time and it just isn't really necessary.


Btw, RAID of any kind is NOT a backup! RAID is redundancy which only protects from drive failure (up to a point). Howevver, drive failure is not the only cause for data loss. User error (such as accidental deletion), viruses and other malware, fire, flood, theft, etc. can all result in lost data. The ONLY way to reasonably ensure the safety of data is for it to exist physically in three separate places. Usually this is on the computer, on an onsite backup drive, and on an offsite backup drive. A backup drive must be kept powered down, disconnected from the computer, and stored out of sight of the computer to be a true backup drive.


If you friend still insists on wanting to run a RAID, then RAID 6 would be safer than RAID 5 since as many as two drives can fail without data loss.



As long as anyone is oppressed, no one will be safe and free.

One has to be proactive, not reactive, to ensure the safety of one's data so backup your data! And RAID is NOT a backup!


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