Any way to set up L1 on disk instead of RAM?

[santiagocastro]

Hi guys!

I'm interested on having L1 cache on disk instead of RAM, because I have seen L1 cache writes back data at a slower rate than direct ones.

My data storage is a slow RAID6, and when writing big ammounts of data, IO reads experiment a very high latency. The only way I found to increase read speed when writing is using L1 cache, but RAM is not big enough to mitigate this efect. L2 cache is not working in write back mode (why?), so it is'nt useful for me.

I tried this .swdsk configuration with v8.0.8730 with no luck:

[...]
<caching>
<cache type="write-back" size="20" units="GB" level="1">
<storage_ref id="1"/>
</cache>
</caching>
[...]
<storage id="1" name="My Computer\C\CACHE\CACHE.img" type="file">
<interval size="20" units="GB"/>
</storage>
<storage id="2" name="My Computer\S\TEST\TEST.img" type="file">
<interval size="5" units="TB"/>
</storage>
[...]

Any suggestions are welcome!

[Ironwolf]

L1 cache writes back data at a slower rate than direct ones

L2 cache is not working in write back mode (why?), so it is'nt useful for me

If Memory L1 WB cache is slower then Direct write, so SSD L2 WB seems like it would be even slower then Memory L1 WB
How much slower is Memory L1 WB cache vs Direct write?

I'm interested on having L1 cache on disk instead of RAM

When creating the Virtual Disk, select n/a for Memory L1, and then create a L2 on the SSD (WB is coming back in a later release).
This would essentially be a L1 on SSD, as there is no L1 in memory, and if L1 is slower then Direct, L2 is likely to slower as well.

recommendation for a 5TB disk, you should be using a SSD cache set at 512GB, and a memory cache set at 51GB

but RAM is not big enough

what about your SSD?

Have you tried the LSFS thin provisioning it's very suitable for RAID 5-6, if you don't use deduplication, its memory requirements are very light.
And likely to get better speed from your RAID 6 on writes

[darklight]

Since we are talking about device header files here, have you tried changing cache settings in the header file?

Code: Select all

          <cache type="write-through" size="1" units="GB" level="2">
            <storage_ref id="2"/>
          </cache>

I believe it is possible to change the type="write-through" into type="write-back". And see what happens. No idea if it works, but why not to give it a try?

[Anatoly (staff)]

@Ironwolf, do you have any update for us please?

[Ironwolf]

I do, ill bee e-mailing the reply soon...

[Anatoly (staff)]

Yup, I see you worked with Alex. Anything else that community might be helpful with?