Advice for cache configuration (backing 2 x LSI 9211-8i)

[Asgaroth]

Hi All,

I've just stumbled upon primocache and am about to evaluate it before purchasing. I'd like to pick the brains of more experienced primocache users out there with regards to how to configure it.

What I currently have is as follows:
[1] an M.2 SSD as my boot drive running Windows 10.
[2] 2 x LSI 9211-8i in IT mode, each with:
[a] 3 x 4TB 7200RPM HDD
2 x 128GB SSD
[c] 1 x 256GB SSD
[d] 1 x 500GB 5400RPM HDD

The LSI 9211-8i does not have any cache on board and can have some poor write performance (I've only just installed these cards so have no metrics myself)

What I was thinking of doing:
[1] 4 x 128GB SSD striped volume assigned for L2 Cache
[2] 6 x 4TB HDD configured for two-way mirror in M$ Storage Spaces (games/video/pictures/work VM's etc)
[3] 2 x 256GB SSD configured as simple volume in M$ Storage Spaces (mainly for games)
[4] 2 x 550GB 5400RPM HDD two-way mirror in M$ Storage Spaces (used for critical backups)

My system is an Asus Z-170 with 32GB memory and an i7 processor which I use primarily for work, but have been known to play a few games, it's now also going to become the home general server (old one was shut down due to multiple component failures).

I was thinking of allocating the following for primocache in front of the 6 x 4TB HDD volume:
[1] 8GB L1 cache (write only - 10 second delay)
[2] Max L2 storage comprised of 4 x 128GB SSD's (read cache)

Does this configuration look okay or would you have any better suggestions as I'm totally new to primocache.

Any tips/tricks would be greatly appreciated.

[Support]

Well, I think this configuration looks okay. You may tune it later at any time according to statistics. Just note that Defer-Write has the risk of data-loss on power failure, system crash or hang. So you shall not enable Defer-Write for volumes which store important data.

[Asgaroth]

Hi,

Thanks for the tip about defer-write, I have disabled it now.

Another quick question, When/how does the L2 write cache work, I'm not seeing L2 cache write statistic climbing when running some benchmarks.

I have primocache 3.0.0 beta setup as follows:
L1 Cache = 8GB (Read Only)
L2 Cache = 95% Read (424 GB) and 5 Write (22 GB)
Gather Interval = Fast (1 Second)

Primocache is setup to cache my data volume which lives on the LSI 9211-8i's.

When I run CrystalDiskMark I can see that when it does its read testing it hits primocache first 99.6% hit ratio, but, when it performs its write test, it does not utilize the L2 write cache at all, an sequential writes are at the speed of 1 SATA disk (155MB/s), 4K ops die in speed (1MB/s). I was expecting the write operations to hit the L2 write cache thereby having a higher write speed.

How does the L2 Write cache work in 3.0.0 beta, is it expected that a write operation will first write to the L2 write cache, and then silently flush its buffers to the volume it is caching in the background? I hope this is how it is supposed to work

The LSI 9211 controllers have no cache on them so it would be great to have primocache running as a cache in front of the volume(s) that exist on the LSI controllers. I'm hoping to have write operations hit the L2 write cache first and then, hopefully, stream the write cache back to the SATA disks sequentially thereby improving the disk write performance.

Disk bench screenshot:



Primocache Settings Screenshot:



Any thoughts/tips/suggestions are appreciated.

[Support]

I'm sorry for the late reply!
When Defer-Write is disabled, write-data will be immediately written to underlying disks, so the write speed will not be improved.

[Asgaroth]

thanks for the info, with regards defer-write, if defer-write is enabled, does that mean that write data is immediatly written to the L2 write cache, and then written to the disks behind primocache after the defer-write timer? For example, if I set defer write to 10 seconds, and write requests occur for the volume primocache is caching, does the write operation immediatly persist to the l2 write-cache, and then, after 10 seconds, get flushed to the volume?

What happens if w read request comes in when the data its looking for resides on the l2-write cache (it has not been written to the volume yet), will it be read from the l2 write cache?

Is the l2 write-cache persisted across system reboots?

[Support]

With Defer-Write on, write-data will be immediately written to cache (L1, or L2 if you don't have L1 write cache or L1 write cache is full). The latency determines the interval that PrimoCache flushes all deferred data to underlying volumes. That is, every latency value, PrimoCache will start the flush process. For more information, please see
http://www.romexsoftware.com/en-us/prim ... on.html#dw

What happens if w read request comes in when the data its looking for resides on the l2-write cache (it has not been written to the volume yet), will it be read from the l2 write cache?

yes.

Is the l2 write-cache persisted across system reboots?

not 100%.