Hot Swap SSD for HDD in a RAID 1 array
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@Dashrender said:
@travisdh1 said:
What does @scottalanmiller always preach about taking advice from someone trying to sell you something?
OK I'll take the hit on that one.
But I still think it's OK to do what the OP wanted as a way to move to SSDs.
Yes, Paul's way of doing it is really not a problem.
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@scottalanmiller Interesting. It has 4GB at the moment. I certainly could up the memory pretty easily. I have a second DC, so I could just take it down, add more RAM and reboot in about 10 minutes. How much do you think?
Here's the stats:
Disk Throughput 12.00 MB/s Average IO size Read: 40.82 KB / Write: 24.63 KB
IOPS 4 at 95% Average Latency 5 ms Reads and 4 ms writes
Read/Write Ratio 86% / 14% Average Queue Depth 0.11
Total Local Capacity 68.00 GB Peak/Min CPU 10% / 0%
Free Local Capacity 36.00 GB (53%) Peak/Min Memory 2.49 GB / 0.91 GB
Used Local Capacity 32.00 GB (47%) Peak/Min Memory In Use 3.28 GB / 1.70 GB -
@pchiodo Where is the IOPS number, I only see a 4. I think that it got cut off.
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@scottalanmiller Here is a link to the stats - It's the total read latency that's raised this issue in the first place.
EDIT: So, if it's memory that's causing this in the first place, I should just be able to increase RAM, and not have to swap drives, correct?
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@pchiodo said:
@scottalanmiller Here is a link to the stats - It's the total read latency that's raised this issue in the first place.
You actually have an IOPS at 95th Percentile of.... 4. Not 4,000.... just 4. This is the lowest IOPS I've ever heard of. Literally.
That latency is because your disks are likely spinning down and going to sleep.
Typically you move to SSD because you have pushed your disks beyond the IOPS that they can do. That's not an issue here. Each drive can deliver 100 - 200 IOPS easily with disk cache pushing bursts much higher.
Dont' go to SSD, it wouldn't do anything for that system. It's idle and running out of memory as it is. The disk latency might be "high", but it is never going to disk.
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@pchiodo said:
EDIT: So, if it's memory that's causing this in the first place, I should just be able to increase RAM, and not have to swap drives, correct?
Doesn't look like there is an issue there, either. You are never hitting the disks.
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@pchiodo said:
@travisdh1 - We have a pretty heavy reliance on the DC, more notably the DNS due to some in house app dependencies. Our performance results from recent DPACK testing showed that this DC would benefit from SSDs vs HDDs.
Are you feeling a lag in AD and DNS? What is pushing you to improve the performance of this system? The DPACK doesn't provide performance information, if provides capacity planning information only. The DPACK shows that the current system is underutilized, not taxed at all. The end users should be providing the feedback as to if the system is performing too slowly, are they complaining?
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@scottalanmiller We occasionally have issues on the shop floor with relatively slow response (4-5 seconds vs. sub-second) and when we track it down, it always points to name resolution as the hang-up. We have a shop floor app that uses hostnames, and seems to hit the DNS quite frequently. Like I said, on occasion, this will appear to slow down, and cause these intermittent lags.
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@pchiodo said:
@scottalanmiller We occasionally have issues on the shop floor with relatively slow response (4-5 seconds vs. sub-second) and when we track it down, it always points to name resolution as the hang-up. We have a shop floor app that uses hostnames, and seems to hit the DNS quite frequently. Like I said, on occasion, this will appear to slow down, and cause these intermittent lags.
DNS resolution of internal machines or DNS resolution of external domains? Even having 100,000 internal machines a DNS table should be in memory and essentially instant. If DNS is a delay, likely something is wrong that needs to be fixed, not that the system isn't fast enough.
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@scottalanmiller Well, I guess I will have to dig further. I don't have any glaring DNS errors, and everything else works fine. Might have to point at the programming people and dig through that. The DBMS, and the Application server for the Shop floor app run exceptionally well, and we have never had an issue with performance on those. But, I suppose this could be a client side issue.
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@pchiodo could be client side, could be hitting a DNS entry that is missing, could be going to something external that has a delay while it waits for remote machines to respond.
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pchiodo - Is your app only looking for local DNS enteries, or also looking for internet based entries as well?
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@scottalanmiller We had an issue where jquery was calling to the web, and we addressed that a couple of weeks ago. I do not think there are any other calls to the outside web.
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@pchiodo said:
@scottalanmiller We had an issue where jquery was calling to the web, and we addressed that a couple of weeks ago. I do not think there are any other calls to the outside web.
Could be calls going through the DC's DNS but need to resolve externally for some reason, too.
