What volume files are not cached by default?

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error-id10t
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Re: What volume files are not cached by default?

Post by error-id10t »

Quick question I'm hoping someone can clarify.

I'm using the latest BETA (Disk not Volume) with 16KB block size, LFU, 4GB cache and write-only (defer write at 10800 seconds). It all appears to be working and if I use something like CDM it shows 80GB as total write bytes but only 400MB as deferred writes with ridicolous speeds.

The thing I don't understand is how do you see what this caches? I'm using sysinternals Process Monitor to check what is being written, it's filtered to only shows writes. If I open up IE8 or Office 2010 as an example, I can see those processes writing to the c:\ drive. When I check the actual files (logfile etc) on the c:\ drive, their date/time stamp has updated as having just been written to. I can also see lot of writes from Mcafee program and when I check those, they are being updated on the c:\ drive with a new time stamp.

Have I misunderstood how this program works, as I would have thought the files would not have been updated until write-defer time occurs or manual dump is done?

Also, many of the system files are being continuosly updated such as the below, does this avoid caching system files all-together?

$logfile
$MFT
eventlog files
$Directory
$BitMap
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Re: What volume files are not cached by default?

Post by Support »

The write data you monitored via sysinternals Process Monitor were in cache first and not actually flushed to the disk if the defer write time hadn't occurred.
error-id10t wrote:Have I misunderstood how this program works, as I would have thought the files would not have been updated until write-defer time occurs or manual dump is done?
Windows and all other applications believe the file is written and updated, however the actual write process to the physical disk haven't occured yet. The data is still in the cache and will be written to the physical disk later. That's why it is called defer-write. You might simply treat the fancycache as an internal disk cache of the physical disk.
error-id10t wrote:Also, many of the system files are being continuosly updated such as the below, does this avoid caching system files all-together?

all the files will be cached. If these files are being continuosly updated, then they will benefit from the defer write because only the latest update data will be finally written to the physical disk in a defer time.
error-id10t
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Re: What volume files are not cached by default?

Post by error-id10t »

support wrote:Windows and all other applications believe the file is written and updated, however the actual write process to the physical disk haven't occured yet. The data is still in the cache and will be written to the physical disk later. That's why it is called defer-write. You might simply treat the fancycache as an internal disk cache of the physical disk.
Thanks for your responses, makes sense. One more question if I may; what you're saying there are no other tools besides it's own Performance Monitor which can show the files are actually in the cache? Both Sysinternals Process Monitor and Windows Explorer are not showing 'reality', they believe the file is being updated and hence show the time/date stamp updated also?

I've had this program running since my last post with the settings posted: one of the 'problems' I have is that the Read Hit Rate is very low at 1%, while write-deferred shows 50% (1GB of writes were saved from being written to the disk).

The Read Hit Rate could be low because it's mainly dealing with files that are being written/updated to and not read from at all of course. But this is one of the reasons I'm curious if there is any other program besides itself, that can show what was cached?
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Re: What volume files are not cached by default?

Post by Support »

error-id10t wrote:what you're saying there are no other tools besides it's own Performance Monitor which can show the files are actually in the cache? Both Sysinternals Process Monitor and Windows Explorer are not showing 'reality', they believe the file is being updated and hence show the time/date stamp updated also?
I am sorry that I shall not use "all other applications"... I used it just for simplification...Of course there can be some tools to monitor the data transfer between system and physical disk at a lower level.
ok, let's make it more clear.
First of all, the information of time/date stamp is also taken as written data.
I drawed a concept diagram as below,
DeferWrite.png
DeferWrite.png (7.74 KiB) Viewed 5973 times
1) Windows or applications write data to files, including time/date stamp information. This data is intercepted by FancyCache and is hold in cache.
2) Users checks the file content/timestamp which triggers Windows/Applications to read file content or time/date information. FancyCache provides the information for the benefit of the physical disk.
3) FancyCache finally writes data to the disk according to the deferwrite algorithm. Third-party tools at this level can monitor the data tranfer.

So you can also find why you still have read hit (1% in your case) when the cache strategy is Write-Only. The read hit was coming from step 2.

Hope these help.
error-id10t
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Re: What volume files are not cached by default?

Post by error-id10t »

Thanks vm for the above.

The Read Hit rate is higher depending what I do ... load a game the second time, it's coming from the cache and Hit rate rises of course. That 1% is mainly when I'm idling and/or just using internet.
magic-man
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Re: What volume files are not cached by default?

Post by magic-man »

I think the read hit rate will be low since you said you are running the cache as write only, so only data that has actually been written is cached for re-use. We have to remember... 95% of Windows normal operations are reads. Personally, I would run the 4 Gig cache ae read-write, LFU algorythm.
error-id10t
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Re: What volume files are not cached by default?

Post by error-id10t »

I'm now running Read+Write cache at 4GB with 3hour write-defer (LFU) at 16KB block size (defaults to 32KB but I'm giving smaller size a go to see if there's any performance improvement, don't mind if there's a small increase with overhead).

No issues with this todate. Does anyone know what might happen during a BSOD? I'm thinking as a reboot keeps the cache, it wouldn't have an impact (unless FancyCache itself fell over completely)?
fsommer1968
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Re: What volume files are not cached by default?

Post by fsommer1968 »

You will loose the data that are in the cache but not already synced to the disk before the BSOD occured. If things are going worse the filesystem is corrupt.
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