RC L2 Cache

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kspare
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Thu Mar 27, 2014 8:53 pm

We're not really interested in the lsfs function as we just won't have enough ram, how is the L2 cache and thick disk working?
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anton (staff)
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Thu Mar 27, 2014 10:28 pm

No deadly issues reported so far. Minor mods actually compared to V6 in terms of this functionality.
kspare wrote:We're not really interested in the lsfs function as we just won't have enough ram, how is the L2 cache and thick disk working?
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Anton Kolomyeytsev

Chief Technology Officer & Chief Architect, StarWind Software

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kspare
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Fri Mar 28, 2014 3:30 am

wont the l2 cache make a huge improvement to our iscsi disks?
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anton (staff)
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Fri Mar 28, 2014 11:18 am

Flash-based write-back cache is going to make a huge difference in performance. Especally after we'll make it surviving reboots.
kspare wrote:wont the l2 cache make a huge improvement to our iscsi disks?
Regards,
Anton Kolomyeytsev

Chief Technology Officer & Chief Architect, StarWind Software

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kspare
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Fri Mar 28, 2014 1:48 pm

I'm just doing some tests.

We have 8 2tb sata drives in raid 5, 64gb ram, lsi controller with cache cade enabled running 4 256gb ssd drives and a PCIx 120gb ssd drive.

Running thick with 48gb l1 cache and 110gb l2 cache we are seeing some interesting results moving vm's on and off the san.

Moving off of the san we saw speeds up to 6.2gb/s moving on we are seeing speeds at around 2gb/s using intel 10gb adaptors.

62% utilization is pretty awesome!

We're moving from an hp server with 8 300gb sas 10k drives.

Here's where it gets weird. While copying a vm onto the san, if we start to copy another vm off of the san back to the same server we see the speeds drop to 500mb/s or 0.5gb/s

That seems like a major flaw? If we have one process running at a time it works good.

How do you put multiple vms on the same if it can't handle multiple reads and writes?
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Alex (staff)
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Fri Mar 28, 2014 6:20 pm

Tank you, we'll investigate such scenario closer.

The first thing that comes in mind ind this case is that disk subsystem is a bottleneck.
When cache is full or doesn't contain required data, we still need to access disk. Sequential disk reads or sequential disk writes are fast, but when we run both these loads at a time, disk load becomes random read-writes. Once again, it is top-of-mind thought and we will check l1+l2 cache performance with pattern like you have described.
Best regards,
Alexey.
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kspare
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Fri Mar 28, 2014 8:51 pm

I think our PCI disk is defunct. I pulled 2 of the ssd's out out of the cachecade volume as we had 4 and i'm testing with that.

Two intel ssd's mirrored are just as fast as 8 sata drives...pretty crazy.

So if we have to reboot the san or we don't survive a power outage we will loose whatever is in the l2 cache?
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anton (staff)
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Fri Mar 28, 2014 10:06 pm

Can you share some numbers so we could tell for sure?

For now - yes, L1 (obvious) and L2 content would be discarded. But we'll make L2 resistant soon :)
kspare wrote:I think our PCI disk is defunct. I pulled 2 of the ssd's out out of the cachecade volume as we had 4 and i'm testing with that.

Two intel ssd's mirrored are just as fast as 8 sata drives...pretty crazy.

So if we have to reboot the san or we don't survive a power outage we will loose whatever is in the l2 cache?
Regards,
Anton Kolomyeytsev

Chief Technology Officer & Chief Architect, StarWind Software

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