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Splitting SSD for L2 cache/ aborted writes/ PerfectDisk

Posted: Thu Oct 03, 2019 7:56 pm
by Xyzzy
Hi.

Scenario:
- SSD as L2 cache
- 1st task read-only
- 2nd task read-write

Questions:
- Should I allocate only fe. 80% of capacity of the SSD for L2 volume in order to avoid slowdowns that happen with full SSD?
- For both tasks, should I just select the L2 volume and size MAX? Or should I rather provide some percentages?

Extra questiona:
- Say SSD write cache has not been written completely to disk because of system shutdown or power failure. Can I expect write to be completed on next power up, so that the state on HDD matches the state on SSD?
- Is it safe to use tools like PerfectDisk on cached drives? Should the cached drives be treated just like physical HDDs?

Re: Splitting SSD for L2 cache/ aborted writes/ PerfectDisk

Posted: Wed Oct 09, 2019 6:48 am
by RobF99
I will only answer the PerfectDisk question. I actually create UltimateDefrag and I can say categorically that it is perfectly safe to defragment drives that are cached with PrimoCache. In fact, it makes defragmentation run at about twice the speed. The reason being is that regular defragmentation does not do any file buffering as it moves files yet PrimoCache does cache the files as it moves them making for much faster reads and writes. It also has the benefit of caching the defragmented files so gives you an added performance boost after defrag since most moved and defragmented files are now cached.

Another way to give your system a quick boost using defrag is to simply run analyze with your defragmenter. In performing the analysis, the defrag program reads the entire MFT. This has the effect of PrimoCache then caching the entire MFT. Makes file lookups etc by the file system much faster so your entire system becomes much faster just from caching the entire MFT.

Re: Splitting SSD for L2 cache/ aborted writes/ PerfectDisk

Posted: Fri Oct 11, 2019 7:44 am
by support
Xyzzy wrote:
Thu Oct 03, 2019 7:56 pm
Should I allocate only fe. 80% of capacity of the SSD for L2 volume in order to avoid slowdowns that happen with full SSD?
It depends on the SSD type/model. SSDs using new technology like optane may not need to reserve certain amount of space.
But yes, generally this is a good practice.
Xyzzy wrote:
Thu Oct 03, 2019 7:56 pm
For both tasks, should I just select the L2 volume and size MAX? Or should I rather provide some percentages?
If you have only one L2 volume, you shall specify the size for one cache task, and then you can use the MAX for the other task. When you use the MAX value for a cache task, it will occupy all remaining L2 volume space.

Re: Splitting SSD for L2 cache/ aborted writes/ PerfectDisk

Posted: Fri Oct 11, 2019 7:51 am
by support
Xyzzy wrote:
Thu Oct 03, 2019 7:56 pm
- Say SSD write cache has not been written completely to disk because of system shutdown or power failure. Can I expect write to be completed on next power up, so that the state on HDD matches the state on SSD?
Sorry, so far no. The data will be lost as the ram cache.

Re: Splitting SSD for L2 cache/ aborted writes/ PerfectDisk

Posted: Wed Nov 06, 2019 4:14 pm
by Xyzzy
support wrote:
Fri Oct 11, 2019 7:51 am
Xyzzy wrote:
Thu Oct 03, 2019 7:56 pm
- Say SSD write cache has not been written completely to disk because of system shutdown or power failure. Can I expect write to be completed on next power up, so that the state on HDD matches the state on SSD?
Sorry, so far no. The data will be lost as the ram cache.
But PC DOES delay shutdown until cache is cleared? Say I have just completed 10 GB write that goes to 10GB SSD write cache and immediately selected shutdown- is it safe?

Re: Splitting SSD for L2 cache/ aborted writes/ PerfectDisk

Posted: Wed Nov 06, 2019 4:35 pm
by support
Xyzzy wrote:
Wed Nov 06, 2019 4:14 pm
But PC DOES delay shutdown until cache is cleared? Say I have just completed 10 GB write that goes to 10GB SSD write cache and immediately selected shutdown- is it safe?
Yes, PrimoCache makes sure that all deferred write-data will be written on normal shutdown. It's safe.
For unexpected shutdown caused by sudden power-loss, bsod, etc, PrimoCache has no time and chance to write data.