RAID on SSD's
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@ccwtech said in RAID on SSD's:
... But I do have another question... For SSD's...
If you are doing RAID 5, would you ever use that as a boot volume? Or do a RAID 1 for boot and RAID 5 for data?
OBR5 (One Big Raid 5). Having drives for the hypervisor alone is such a waste, it's not like the box is going to be rebooting every 5 minutes. You'll get better performance and capacity by using OBR5.
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@travisdh1 said in RAID on SSD's:
@ccwtech said in RAID on SSD's:
... But I do have another question... For SSD's...
If you are doing RAID 5, would you ever use that as a boot volume? Or do a RAID 1 for boot and RAID 5 for data?
OBR5 (One Big Raid 5). Having drives for the hypervisor alone is such a waste, it's not like the box is going to be rebooting every 5 minutes. You'll get better performance and capacity by using OBR5.
Even if it was - what difference would that make? Why waste drives and drive bays for booting a hypervisor (or an OS)?
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For some reason I recall that booting to a RAID 5 was unreliable (shouldn't do), but it's been so long since I have worked with RAID 5 I'm not sure where I heard that.
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@ccwtech said in RAID on SSD's:
For some reason I recall that booting to a RAID 5 was unreliable (shouldn't do), but it's been so long since I have worked with RAID 5 I'm not sure where I heard that.
I do not/have not had this experience.
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@ccwtech said in RAID on SSD's:
For some reason I recall that booting to a RAID 5 was unreliable (shouldn't do), but it's been so long since I have worked with RAID 5 I'm not sure where I heard that.
RAID 5 on HDD is unreliable today, and shouldn't ever be used. SSD drives don't have the same issues. That might be what you're remembering.
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@travisdh1 said in RAID on SSD's:
@ccwtech said in RAID on SSD's:
For some reason I recall that booting to a RAID 5 was unreliable (shouldn't do), but it's been so long since I have worked with RAID 5 I'm not sure where I heard that.
RAID 5 on HDD is unreliable today, and shouldn't ever be used. SSD drives don't have the same issues. That might be what you're remembering.
I believe so as well.
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@travisdh1 said in RAID on SSD's:
@ccwtech said in RAID on SSD's:
For some reason I recall that booting to a RAID 5 was unreliable (shouldn't do), but it's been so long since I have worked with RAID 5 I'm not sure where I heard that.
RAID 5 on HDD is unreliable today, and shouldn't ever be used. SSD drives don't have the same issues. That might be what you're remembering.
While I agree that it shouldn't be use - it's not because it's unreliable. It's because it's changes of running into a URE during a resilver is very high depending upon the size of the array (i.e. if the array is 12TB or higher, the chances of having an URE during rebuild is near 100% on consumer drives, or 120 TB on enterprise class drives)
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@ccwtech said in RAID on SSD's:
For some reason I recall that booting to a RAID 5 was unreliable (shouldn't do), but it's been so long since I have worked with RAID 5 I'm not sure where I heard that.
That was never a RAID issue. You are thinking of a specific problem with any non-RAID 1 on software RAID where you can't boot to RAID before the RAID has been created. It's nothing to do with the RAID but with the boot sector not existing until after the RAID has been created. Chicken and egg problem. RAID 1 gets around this by having a full copy of the entire boot sector on every disk in the array.
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Would a RAID 6 be better for the extra redundancy?
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@ccwtech That additional parity creates a lot of complication (calculation-wise). I haven't seen Raid 6 offered as a solution unless you really need double the parity capacity--which I've never experienced needing personally but I know is out there
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So for greater redundancy RAID 10?
Is the reason for 5 vs. 10 just the cost of the extra drive?
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@ccwtech said in RAID on SSD's:
So for greater redundancy RAID 10?
Is the reason for 5 vs. 10 just the cost of the extra drive?
Yes, it's a much bigger cost on SSDs.
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@ccwtech said in RAID on SSD's:
Would a RAID 6 be better for the extra redundancy?
RAID isn't that simple. Does the cost for extra parity make sense?
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@scottalanmiller said in RAID on SSD's:
@ccwtech said in RAID on SSD's:
Would a RAID 6 be better for the extra redundancy?
RAID isn't that simple. Does the cost for extra parity make sense?
Was looking at the fact that you can lose 2 drives (not just one) as an extra safeguard. But in a 4 drive SSD RAID 10 makes more sense to me than 6.
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@ccwtech said in RAID on SSD's:
@scottalanmiller said in RAID on SSD's:
@ccwtech said in RAID on SSD's:
Would a RAID 6 be better for the extra redundancy?
RAID isn't that simple. Does the cost for extra parity make sense?
Was looking at the fact that you can lose 2 drives (not just one) as an extra safeguard. But in a 4 drive SSD RAID 10 makes more sense to me than 6.
It does, but you have to invest in double the HD's for the same capacity. If redundancy is your only concern then Raid 10.
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@ccwtech said in RAID on SSD's:
@scottalanmiller said in RAID on SSD's:
@ccwtech said in RAID on SSD's:
Would a RAID 6 be better for the extra redundancy?
RAID isn't that simple. Does the cost for extra parity make sense?
Was looking at the fact that you can lose 2 drives (not just one) as an extra safeguard. But in a 4 drive SSD RAID 10 makes more sense to me than 6.
That's not a way to measure RAID reliability. I actually a video about why we never mention "number of lost drives" in the SAMIT queue.
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@scottalanmiller said in RAID on SSD's:
That's not a way to measure RAID reliability. I actually a video about why we never mention "number of lost drives" in the SAMIT queue.
Which one? You have several RAID videos.
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@ccwtech said in RAID on SSD's:
@scottalanmiller said in RAID on SSD's:
That's not a way to measure RAID reliability. I actually a video about why we never mention "number of lost drives" in the SAMIT queue.
Which one? You have several RAID videos.
It's in the queue, not visible yet. It's specifically about why we don't look at "how many drives can be lost"
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@scottalanmiller said in RAID on SSD's:
@ccwtech said in RAID on SSD's:
@scottalanmiller said in RAID on SSD's:
That's not a way to measure RAID reliability. I actually a video about why we never mention "number of lost drives" in the SAMIT queue.
Which one? You have several RAID videos.
It's in the queue, not visible yet. It's specifically about why we don't look at "how many drives can be lost"
Ahhh, ok. -
@francesco-provino said in RAID on SSD's:
@ccwtech said in RAID on SSD's:
I set up my servers with RAID 10 and 10 or 15 K RPM Drives and a dedicated RAID card and an SSD Drive for CacheCade.
However with the decrease in pricing for SSD drives, I would like to start using them more in servers.
- Still do RAID 10 with SSD's?
- Is a dedicated RAID card still needed if using SSD's?
- Usually RAID 5 makes sense. Still RAID 10 if you want maximum performance. Be aware that you can saturate almost any SATA/SAS controller with the performances of 6-7 SSD.
- Apply the same consideration for the HDD.
I actually came here to ask about #1 - is that 6 drives in raid10? Has anyone measured this / tested it etc?
