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Can "latency=infinite" setting work?

Posted: Thu May 30, 2013 10:44 am
by tekken
Hello :!:
Please tell me what value of latency I must configure for deferwrite in fancycache if I want next algoritm:
I want to write data from cache to hdd only when cachesize is full. And only when cachesize is not enought for new writeback data, oldest data must be write from cache to HDD.

For example In SuperCache program latency can be infinite (-lw infinite). And when infinite, write data are written to the cache only as required to make new cache mappings. As old pages age, they become eligible for cleaning to be reused for new mappings.

P.S. If I set latency=86400000 (1000days) it will be my solution? And I must choose LRU (Least Recently Used) for my task? Not LFU (Least Frequently Used)?

P.S.S. sorry for my russian-english :oops:

Re: Can "latency=infinite" setting work?

Posted: Fri May 31, 2013 6:17 am
by Nina
You have to set Latency as high as possible and that's it.. and yes, LRU is for you..

SuperCache is a stupid in it's own logic, there is no way to read blocks from write buffer .. since they should be committed to physical drive before any read operations.. and that's why FancyCache is a great solution at least for me ^_^.

Re: Can "latency=infinite" setting work?

Posted: Fri May 31, 2013 3:10 pm
by Incriminated
Ok so i see benefit in that high latency strategy for high amount (i.e. +5GiB of L1-cache) for OS-SSDs,

But what about when using read and Write-Cache with small amount of L1-cache (i.e. 1GiB) for a storage HDD.
I think it would be better to start writing immediately, because when i write 10GB... within 10 secs the buffer runs full, by that means within that 10secs i could have flushed another up to 1Gib off to the drive (assuming write rate of ~100MB).. giving me double the accelaration for 10GB-transfers.

Is latency 0 allowed?

Or does it start flushing to disk automatically when buffer runs full? I think it does that, but im not sure.

How does Averaging Write Amount affects that in detail. I see the explaination is a little weak, giving me no idea if in my scenaria it may be of usage/benefit.

Re: Can "latency=infinite" setting work?

Posted: Wed Jun 12, 2013 1:31 pm
by dustyny
Tekken - Unless you are using this with temp data it's a really bad idea.. probably the worst thing that you can do with F.C.

Incrimninated - What you are asking is what happens when set no write delay at all.. which is the best possible use for F.C.

Keep in mind in most cases Write delay just hides a status bar. In very specific settings (such as a scratch disk for Photoshop, or a rendering temp file for videos) it will speed things up at the expense at putting that data at risk. yes there are ways to mitigate that risk but it doesn't eliminate it. I have corrupted data with F.C (Vmware VMDKs are not very resilient) but I had a backup ready for a quick restore.

Re: Can "latency=infinite" setting work?

Posted: Wed Jun 12, 2013 2:02 pm
by Incriminated
Yup had my first bluescreen with FC this morning when clicking on a folder of a spinned down (suspended) drive.

It booted, but most of my data in my personal folder got corrupted, so in this case i had to reconfigure every programs settings running at the time of the BSOD.

What Timeout do you recommend for a Boot-OS-SSD= SHould i take very high timeout (x-days) or small (10secs) or even none? I really dont know.