SSD cache for Win8 Storage Spaces

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fpdragon
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SSD cache for Win8 Storage Spaces

Post by fpdragon »

Hi,
First, I want to say that this app is exactly what I was searching for. Thanks!
But there are some problems with my system and I am hoping someone can help...

My System:
*) Super Talent SSD 260GB (C: for System and D: for Cache)
*) about 10 HDD from 500GB to 3TB used as Win8 Storage Spaces Parity Storage (short: kind of flexible RAID5)

The problem with Storage Spaces is that I can't reach a higher write speed than about 25MB/sec. That's slow. :-(

The plan was to speed up the writing with a SSD cache. So I configured 60GB from D: as L2 cache.

So from my understanding I need the "Defer Write" feature to build up my write cache. For "Latency" I configured 1800seconds (an half hour). I want to be able to copy 60GB data with filling up the cache and no speed drop. The files can be stored to the storage space when ever the pc has time for it.

Now to the Results:
I'm seeing that FancyCache is doing something and in the first seconds it is definately fast (200MB/s).
But after some GBytes the speed drops and varies at 5MB/s to 25MB/s and I don't know why. The cache usage is not higher than 20% and the copy process hasn't took longer than a few seconds. I expected that the speed drops soonest after 30 minutes copying or the L2 cache is full but bothe is definately not the case.
Can somebody explain this?

Second, the copy process of large files stucks after some time and blocks the partition. Thats fatal. I can't stop the caching. I can't stop the copy process. I can't delete the currently copyed files, I even can't use the disk any more in any way. When I open a new explorer window I can select the disk and then it's just searching for files endlessly and no file or folder is shown.
When I try to restart the machine it is "Shutting down" endlessly. The only solution was a hard reset.
Sounds like a bug to me? btw again: Win8 and the disk to speed up is a virtual sorage spaces partition.

At last I have a question:
As I said I am trying to configure a L2 SSD Write cache. It seems that L2 caching is only enabled for Read and Write config. Why is this? Is it because the Defer Write feature is a kind of Read cache? It would be cool if I could configure that the whole SSD cache is used for write only and not for read cache..

I hope someone can help...
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Support
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Re: SSD cache for Win8 Storage Spaces

Post by Support »

Hi fpdragon,

Currently FancyCache doesn't support SSD as write cache. This feature may come out in next versions.
Thanks.
fpdragon
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Re: SSD cache for Win8 Storage Spaces

Post by fpdragon »

Thanks for the answer!

I can't wait for this feature. :-D Would be awesome to have super fast storage spaces.

btw. I interpret you answer as that the SSD is used in the "Read/Write" config also as read cache only and the L1 cache is the only write cache.

thx
dustyny
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Re: SSD cache for Win8 Storage Spaces

Post by dustyny »

fpdragon

I've been using Fancycache with storagespaces for about 4-5 months now and I get extremely fast performance. You can find some benchmark results here..

viewtopic.php?t=1278
fpdragon
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Re: SSD cache for Win8 Storage Spaces

Post by fpdragon »

Thanks for your info but your results seem to be quite equal to mine...

1.) Storage Spaces with Parity has slow write performance. :-(

2.) L1 write cache helps here with awesome write speeds but it is limited by the configured RAM. If the RAM cache gets full, the speed drops to normal.

3.) L2 write cache (SSD Write cache) isn't working right now (that's what "support" has confirmed above) but that would be the absolute killer feature for me. Copying 60GB files with 200 MB/s instead of about 25 MB/s. I'd love to already see this working :-).

Can you agree?
dustyny
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Re: SSD cache for Win8 Storage Spaces

Post by dustyny »

Yes storage space parity is very expensive performance wise but that is always the case. In the RAID days we'd mix different types 5+0 or 1+0 to mitigate this but that gets very costly in disks.

Keep in mind that Storage spaces came from the consumer space and is more of an advanced JBOD solution then a ZFS alternative; they aren't really ready for prime time IMO. There is a lot of weird behavior with them (with performance & how it handles parity) and when they break it's a real pain to get them working again (all done via poorly documented powershell commands). My advice would be to stick with RAID for now and use a RAID calculator to determine the level of parity you need. Use a benchmarking tool to test performance costs, so you can test RAID 50 vs 10, vs 5. Fancycache will mitigate certain issues but even with a ton of SSDs (I use 8) you'll still see low transfer rates. Also keep in mind transferring lots small files like 4K will always be extremely slow compared to transferring very large (4GB) files that's overhead that you can't avoid.

http://www.icc-usa.com/raid-calculator.php
fpdragon
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Re: SSD cache for Win8 Storage Spaces

Post by fpdragon »

thanks for your post but I'd say it is totally off topic.

I do know Storage Spaces and ZFS and numerous other alternatives and it would be a much larger topic to compare them all in detail. I also don't want to discuss the drawbacks of storage spaces. I personally can handle all of them with workarounds and it is (for me and my application) still the best solution on the market.

The idea was to improve the slow write performance of storage spaces and it seems to be already solved with RAM caching and I'm looking forward to see SSD caching with FancyCache to implement larger caches.
dustyny
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Re: SSD cache for Win8 Storage Spaces

Post by dustyny »

I personally can handle all of them with workarounds and it is (for me and my application) still the best solution on the market.
I'm sure you can... :roll:

I wish you the best of luck, make sure you have good backups.. :lol:
turkina
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Re: SSD cache for Win8 Storage Spaces

Post by turkina »

If you have a UPS connected to your Windows server and have it configured to gracefully power down if the UPS detects a power loss, you can use the following command to boost write performance on parity vdisks in Storage Spaces:

Set-StoragePool -FriendlyName <Storage Pool Name> -IsPowerProtected $True

Took my writes from 40MB/s to 138MB/s on 8x Seagate 2TB SATA drives.
dustyny
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Re: SSD cache for Win8 Storage Spaces

Post by dustyny »

Just spent two days fixing 2 broken storage spaces.. decided to drop disks for no reason (yet again)... Yes they are a wonderful alternative to RAID and 100% ready to use for serious work. :lol:
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