What Makes Parity RAID Safe on SSDs
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@scottalanmiller said in What Makes Parity RAID Safe on SSDs:
@dafyre said in What Makes Parity RAID Safe on SSDs:
@scottalanmiller said in What Makes Parity RAID Safe on SSDs:
@marcinozga said in What Makes Parity RAID Safe on SSDs:
Now another thing is most misunderstand what URE is and assume it's a set number and you always hit URE after reading 12.5 TB. It's not, it's just a probability or running into sector on disk that cannot be read from. Similar to playing Russian Roulette, if you're lucky, you can keep pulling the trigger indefinitely without blowing your brains out, you can have RAID 5 rebuilding PBs of data without ever hitting URE.
That's why it's a percentage risk number. Otherwise an array of 12.5TB would have a 100% failure rate, but that never quite happens. There is never 100% success nor 100% failure no matter how big or small the array. But it gets really high, really quickly.
I can honestly say in the dozen or so RAID-5 rebuilds that I've seen in the last 6 years, literally half of them were successful, and the other half were not. This was in arrays of 6 x 250GB drives to 8 x 1TB drives (all Winchester / spinning rust).
That's a rough fail rate.
There for a few years, we had a crazy time with stuff crapping out. Even a new drive array went crazy. After the LeftHand, the RAID 5 rebuilds got better, but still lost far more of them than we should have.
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@Dashrender said in What Makes Parity RAID Safe on SSDs:
I've been lucky I guess - I've never lost an array when resilvering a RAID 5 array.
I'm not actually 100% sure I've ever seen one recover. Seems like I must have, but I can't actually remember it.
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@Dashrender Some RAID controllers have certain limit on number of URE they encounter before marking drive as failed. I had that happen on some LSI controllers, but the numbers were really high, perhaps in thousands.
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@marcinozga said in What Makes Parity RAID Safe on SSDs:
@Dashrender said in What Makes Parity RAID Safe on SSDs:
I've been lucky I guess - I've never lost an array when resilvering a RAID 5 array.
Ha, I've been lucky to never use RAID 5
How long have you been in the game?
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@Dashrender said in What Makes Parity RAID Safe on SSDs:
@marcinozga said in What Makes Parity RAID Safe on SSDs:
@Dashrender said in What Makes Parity RAID Safe on SSDs:
I've been lucky I guess - I've never lost an array when resilvering a RAID 5 array.
Ha, I've been lucky to never use RAID 5
How long have you been in the game?
Long enough. 17 years if my math is correct. I always managed to push RAID 10 over 5.
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@marcinozga said in What Makes Parity RAID Safe on SSDs:
@Dashrender said in What Makes Parity RAID Safe on SSDs:
@marcinozga said in What Makes Parity RAID Safe on SSDs:
@Dashrender said in What Makes Parity RAID Safe on SSDs:
I've been lucky I guess - I've never lost an array when resilvering a RAID 5 array.
Ha, I've been lucky to never use RAID 5
How long have you been in the game?
Long enough. 17 years if my math is correct. I always managed to push RAID 10 over 5.
Wow - so back in the late 90's you were able to always justify the price of RAID 10, great. I wasn't - and really it wasn't needed either.
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@Dashrender I came from heavy gaming background, so performance was always my priority, sometimes the only priority, lol. So RAID 5 was off the table, period. And I was lucky enough to always work for people who had no clue what I was actually doing.
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@Dashrender said in What Makes Parity RAID Safe on SSDs:
I've been lucky I guess - I've never lost an array when resilvering a RAID 5 array.
Me either, technically.
Though I have lost a good percentage just from plugging the new drive in.
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@BRRABill said in What Makes Parity RAID Safe on SSDs:
@Dashrender said in What Makes Parity RAID Safe on SSDs:
I've been lucky I guess - I've never lost an array when resilvering a RAID 5 array.
Me either, technically.
Though I have lost a good percentage just from plugging the new drive in.
This is what triggers the resilver
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@dafyre said in What Makes Parity RAID Safe on SSDs:
@BRRABill said in What Makes Parity RAID Safe on SSDs:
@Dashrender said in What Makes Parity RAID Safe on SSDs:
I've been lucky I guess - I've never lost an array when resilvering a RAID 5 array.
Me either, technically.
Though I have lost a good percentage just from plugging the new drive in.
This is what triggers the resilver
I always thought it was the whining of my users as the server's performance dropped off a cliff lol
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@MattSpeller said in What Makes Parity RAID Safe on SSDs:
@dafyre said in What Makes Parity RAID Safe on SSDs:
@BRRABill said in What Makes Parity RAID Safe on SSDs:
@Dashrender said in What Makes Parity RAID Safe on SSDs:
I've been lucky I guess - I've never lost an array when resilvering a RAID 5 array.
Me either, technically.
Though I have lost a good percentage just from plugging the new drive in.
This is what triggers the resilver
I always thought it was the whining of my users as the server's performance dropped off a cliff lol
You mean you can't hear your users when things are working well? Dang... I need to come work with you.
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@dafyre said in What Makes Parity RAID Safe on SSDs:
@MattSpeller said in What Makes Parity RAID Safe on SSDs:
@dafyre said in What Makes Parity RAID Safe on SSDs:
@BRRABill said in What Makes Parity RAID Safe on SSDs:
@Dashrender said in What Makes Parity RAID Safe on SSDs:
I've been lucky I guess - I've never lost an array when resilvering a RAID 5 array.
Me either, technically.
Though I have lost a good percentage just from plugging the new drive in.
This is what triggers the resilver
I always thought it was the whining of my users as the server's performance dropped off a cliff lol
You mean you can't hear your users when things are working well? Dang... I need to come work with you.
They're too busy "sportsing" or something outside
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@dafyre said in What Makes Parity RAID Safe on SSDs:
@BRRABill said in What Makes Parity RAID Safe on SSDs:
@Dashrender said in What Makes Parity RAID Safe on SSDs:
I've been lucky I guess - I've never lost an array when resilvering a RAID 5 array.
Me either, technically.
Though I have lost a good percentage just from plugging the new drive in.
This is what triggers the resilver
So if the tree never falls in the forest, did it even fall?
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@BRRABill said in What Makes Parity RAID Safe on SSDs:
@dafyre said in What Makes Parity RAID Safe on SSDs:
@BRRABill said in What Makes Parity RAID Safe on SSDs:
@Dashrender said in What Makes Parity RAID Safe on SSDs:
I've been lucky I guess - I've never lost an array when resilvering a RAID 5 array.
Me either, technically.
Though I have lost a good percentage just from plugging the new drive in.
This is what triggers the resilver
So if the tree never falls in the forest, did it even fall?
Did it ever exist?
Edit: Great. Now I'm having an existential crisis.
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Was there even a forest?
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@marcinozga said in What Makes Parity RAID Safe on SSDs:
@Dashrender I came from heavy gaming background, so performance was always my priority, sometimes the only priority, lol. So RAID 5 was off the table, period. And I was lucky enough to always work for people who had no clue what I was actually doing.
Me too - but they my bosses always pushed - can't it be cheaper? And crazy me said, well there is this option with RAID 5 - I probably just should have said - no, it can't be cheaper.
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@Dashrender said in What Makes Parity RAID Safe on SSDs:
@marcinozga said in What Makes Parity RAID Safe on SSDs:
@Dashrender I came from heavy gaming background, so performance was always my priority, sometimes the only priority, lol. So RAID 5 was off the table, period. And I was lucky enough to always work for people who had no clue what I was actually doing.
Me too - but they my bosses always pushed - can't it be cheaper? And crazy me said, well there is this option with RAID 5 - I probably just should have said - no, it can't be cheaper.
Right, because the logic that kept you from telling them that there is no RAID 0 option should have also ruled out RAID 5. It's a very important "business presentation" skill in IT, knowing what to present as an option and what to rule out. The people to whom you are presenting assume that if you present it, even as an out-lier, that you have approved it. Because you'd never say that skipping backups or using RAID 0 or running servers from desktops was an option, right? So if you don't present those, and you do present RAID 5, clearly you are conveying to management that they fall into different categories. Since the category of the first group is "this isn't an option so I can't tell you about it" the category of the second has to be some flavour of "not my top pick but something worth considering is..."
When, in fact, RAID 5 should be part of the first group along with RAID 2, 3 and 4.
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@scottalanmiller that might be worth its own topic.
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@Tim_G
I would go RAID 5 on SSD when i am short on budget, but i need SSD performance.
In case I am capable of going SSD RAID 10, i will -
@Oles-Borys said in What Makes Parity RAID Safe on SSDs:
@Tim_G
I would go RAID 5 on SSD when i am short on budget, but i need SSD performance.
In case I am capable of going SSD RAID 10, i willI'm a little confused by this. Personally I would primarily go RAID 5 on SSD, and only consider going RAID 10 when I need the max performance from the array possible. The IOPs difference between HDD and SDD is staggering. Could you need more than RAID 5 SSD gives? Sure, but that seems more like a fringe case.
