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wondering about raid 5

T

tommo123

Platinum Member
was thinking about getting a 4 bay enclosure but not sure how it works when it comes to failure. if 1 drive fails, you replace it, rebuild and done?

what about if the enclosure fails? i assume you can't connect the drives into a PC and create an array that way until you get a new enclosure? i've read that you cant even put them in a new enclosure as they auto initialise the drives and therefore wipe them - even the same make/model.

in the dead enclosure scenario - how do you get your data back?
 
This information is available all over the web but whatever.

In RAID 5 if one disk fails, you replace it with another of the same size and the array rebuilds to the new drive (data is split up into n-1 number of chunks + 1 parity chunk and spread over all 5 drives).

If you experience a second drive failure at the same time, or during the rebuild, you're screwed. Chances are pretty low unless the failure is due to a power supply surge but there's always that risk.

The RAID info is normally stored somewhere on the drive (I suspect in the Host Protected Area, because I have wiped start and end of the drives and Intel RST has still detected that drive used to be part of an array). So if you place within the same enclosure (or same brand) it is likely that the array will be recognised, but you should check with the manufacturer.

IMO a cheap Intel based RAID and small case is preferable to a NAS, will cost about the same as a good NAS but can double as EG a HTPC or similar. And this way you won't have any issues with RAID detection (I have transferred whole RAID 5 arrays to new Intel chipsets with no issues, they are detected).
 
If one drive fails you're good to go just put in another one. If the enclosure fails, that's where it gets tricky, depends how it works and if it's proprietary. It's one of the reasons I'm not a big fan of hardware raid or proprietary enclosures. Rather use a PC based OS with open source raid solution like mdraid so that I'm not tied to any specific hardware.

But in general if you have good backups the odds of hardware failure at the enclosure level is probably not very high, so on a budget with small disk space/future proofing requirements a 4 bay enclosure is not a bad thing. It beats having a single drive that can fail and take your data with it.
 
Agree, software raid is an advantage here (Windows 7 had built in soft RAID 5 but I think it was removed). I'd be interested to know with regards to if it's possible to migrate a RAID 5 from one system to another (ie. NAS box to Intel RST etc.).
 
it's what i was wondering too mainly. i did read a little online before posting this but it seemed hit and miss whether you could migrate the array or not.
 
If you don't mind sacrificing a little bit more drive capacity, do raid 10. In a four drive array, I have found it much faster than raid 5. Being able to endure potentially up to 2 drive failures can be nice if all drives are from the same lot.

Migrating raid arrays, I have had good success going from card to card that is the same brand and model tier. Meaning don't go from most expensive card to the cheapest.

I have never used dedicated enclosures, but I assume if you go with a reputable brand, they should use the same controller card in each enclosure as long as they are the same model number.
 
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Agree. Suspect that most dedicated NAS are backwards compatible within their range, after all this gives people an upgrade / replacement path.
 
Go RAID6.

In 5, after 1st HDD failure 2nd drive tends to fail during rebuild process. Array is dead if this happens.

RAID6 can tolerate 2 drive failures.

Been there, done that.

Do backups. RAID is for uptime not backups of your stuff.
 
I all depends on your goals. If you want it just to house data, on a 4 drive device I'd probably go with RAID5 over RAID6. If I was going to lose that much space on RAID for a 4 drive device I'd go RAID1+0 for better performance. As said, do backups as that is the only guarantee against data loss.
 
bigi said:
Go RAID6.

In 5, after 1st HDD failure 2nd drive tends to fail during rebuild process. Array is dead if this happens.

RAID6 can tolerate 2 drive failures.

Been there, done that.
Click to expand...
The problem with RAID 6 is that if data recovery is needed, it is a lot more complex and expensive to recovery.

Do backups. RAID is for uptime not backups of your stuff.
Click to expand...
This is very true. With larger drives, the probability of multiple drive failure is significantly greater than with smaller drives of the past. I do a lot o RAID data recovery and I'd recommend a solid backup over double redundancy any day.
 
Yeah you want backups. Raid is for convenience so that when a drive fails you're not dead in the water while you restore data. Depending on nature of data you may need to rebuild permissions/folder structure etc and that can be a huge pain. I do raid for everything including data that may not be that important, like movies. Then I selectively backup what's the most important. When a drive fails I just remove the old one, pop a new drive in, and let it rebuild, and I can continue to access the data.
 
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