What's the largest bytes cached by ReadyBoost that someone can expect with a Windows 7 laptop with 8GB of RAM?

I adding a Class 10, 16GB SD Card, primarily for ReadyBoost, and I haven't seen the cache size go above 3.5GB (out of 12GB allocated).

My usage is 90% Chrome (with dozens of tabs), a bit of Office, text editors, and remote access apps.

If I can't realistically expect it to go over 4GB, I would reduce the space allocated to it, in case I need the space for random tasks (like moving a 10GB file via SD card sneaker net).

Update: After a few weeks of running this laptop, I have spotted ReadyBoost using over 7GB of cache file.

  • What format is the SDCard formatted to? – Ƭᴇcʜιᴇ007 Aug 31 '15 at 18:31
  • I'm not sure it matters, but it's NTFS. I am referring to how much cache is actually USED as reported in Performance Monitor. It creates the 12GB file easily enough. – user2391738 Sep 1 '15 at 19:48

Your question isnt very clear. It sounds like you asking how big a ReadyBoost cache can be on your SD card.

From Technet:

You must reserve at least 256 MB. Larger caches can improve performance, but the ReadyBoost cache cannot be greater than 4 GB on a FAT32 file system or greater than 32 GB on an NTFS file system.

ReadyBoost creates a disk cache file named ReadyBoost.sfcache in the root of the flash drive. The file is immediately created for the full size of the specified cache. However, Windows will gradually fill the space with cached content.

Even if the ReadyBoost cache is filled, that doesnt mean it will read from it. ReadyBoost will use SuperFetch to predict what data you might read in the future. This doesnt guarantee the data it puts in the cache will even be read.

More than likely, on your machine, you are writing lots of data to the ReadyBoost cache, but not actually reading from it. You can see this using PerfMon and adding the counter Cache Read Bytes/sec.

I strongly suggest you read that Technet article, as well as this article. You are getting very little, if any benefit from ReadyBoost on your 8 GB machine.

  • The Cahe Read Bytes/sec, and in fact all of the counters in the Cache section of PerfMon, do not apply to ReadyBoost (or SuperFetch). They apply to the "reactive" file cache. – Jamie Hanrahan Sep 24 '15 at 23:27
  • @JamieHanrahan They absolutely do. "Bytes of I/Os satisfied from ReadyBoost caches per second." – Keltari Sep 24 '15 at 23:57
  • oh, sorry. You're looking at the ReadyBoost counter class. You are correct. Shall we delete all of these comments? I would suggest an edit to your post specifying the ReadyBoost counter class. – Jamie Hanrahan Sep 25 '15 at 0:12

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