I don't like to report this, because it's vague, but it happens frequently when I try to use a large (> 50000 MB) cache. I don't see it happen much with less than that, but the system (2008R2 Enterprise) does have 64 GB of system RAM and theoretically shouldn't "mind" having 50 GB used for cache, right?
When the problem happens, I see symptoms of severe out-of-memory issues in Windows -- buttons and tabs not having labels, programs being unable to start, etc. If I stop the cache, the problem goes away. The system (according to Task Manager) still shows as having 8 or so GB free when it happens. If I am using a write cache, I often end up with files that need to be recovered with chkdsk.
I don't have a clear sense of when this happens; I do seem to need to be hitting the disk fairly hard (simultaneous reads and writes) -- just having the cache running hasn't resulted in the issue. I will report more if I can tell what might be causing the problem a bit better.
Severe memory errors with large write cache
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InquiringMind
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Re: Severe memory errors with large write cache
Does changing block size have any effect (and are you using the default 4KB size)?
Re: Severe memory errors with large write cache
Good point. The block size will affect how much memory overhead there is, which is in addition to the set cache size. (I believe it's also proportional to both the cache size and the size of the disks being cached, so on a large array it could be extremely large.)InquiringMind wrote:Does changing block size have any effect (and are you using the default 4KB size)?
Re: Severe memory errors with large write cache
I have tried several different block sizes; the block size only seems to affect how much memory I can allocate to the cache, not the probability of these errors happening. It only seems to happen with any frequency when I am pushing the cache to as large as I can (before getting "Unable to start cache"), regardless of the block size (though the larger the block size, the larger the cache can be before hitting that limit).
In the past week I've started to learn how much (not) to overallocate the cache. If I can push it up to 50000 MB at the maximum, I don't typically see any issues if I only use 48000 MB. What I don't really understand is that the system reports at least 8 GB free even when I am seeing the Windows out-of-memory errors. It's almost as if there's some boundary issue at 8 GB that is making the system appear to be out of memory.
In the past week I've started to learn how much (not) to overallocate the cache. If I can push it up to 50000 MB at the maximum, I don't typically see any issues if I only use 48000 MB. What I don't really understand is that the system reports at least 8 GB free even when I am seeing the Windows out-of-memory errors. It's almost as if there's some boundary issue at 8 GB that is making the system appear to be out of memory.
Re: Severe memory errors with large write cache
Seems strange...
Usually kernel nonpaged pool and paged pool might be an issue, but I think on Windows 2008R2 they shouldn't be the cause.
Is it possible to make and upload a screenshot of the Performance tab in Windows Task Manager while Windows starts to be out of memory? Thanks.
Usually kernel nonpaged pool and paged pool might be an issue, but I think on Windows 2008R2 they shouldn't be the cause.
Is it possible to make and upload a screenshot of the Performance tab in Windows Task Manager while Windows starts to be out of memory? Thanks.