bug or feature - direct L2 write cache without using L1 ram cache

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minhgi
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bug or feature - direct L2 write cache without using L1 ram cache

Post by minhgi »

PrimoCache version: 3.0.0 beta
Cache Settings: 1GB L1 / 32GB L2 / integrated cache strategy with 10 sec defer write
Windows OS: Windows 10 Creator updates
Hardware Information (CPU/Motherboard/Memory/Harddisks): Lenovo Yoga12 / Broadwell i7-5600U / 8GB memory / 1TB Toshiba
Description:

So if I use read/write cache strategy for both L1 / L2 and later disable L1 completely, I noticed defer write immediately went to the L2 and then to the hard drive afterward. So if you want to setup a L2 read/write cache only, this would be the way. Great for people that don't have enough memory for L1 cache.

It seem the defer write options are greyed out if you put a zero a value for L1 when setting up a new cache for read and write mode.

May as well make this into a feature set for direct write back to L2 without L1 being enable. Performance is tad less without L1 but just as fast.
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Re: bug or feature - direct L2 write cache without using L1 ram cache

Post by Support »

By default, L2 is pre-set to read-only cache. So when you disable L1 cache, Defer-Write options are greyed because there's no write cache. You need to change L2 to read-write or write-only cache (in Advanced L2 Options, Uncheck Individual Read/Write Space or set certain space for write cache) to enable Defer-Write options.
bright
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Re: bug or feature - direct L2 write cache without using L1 ram cache

Post by bright »

This is definitely a feature, and it is a HUGE advantage imho!
By using only Level2 for deferred writes, we are getting reliable write caching here, raising this product to a whole new level.
Benefit is crash-surviving write cache, a high speed writes that will not be lost on violent computer power-outs.
One can set Level1 cache to be 100% read, and give Level2 cache certain write percentage (by default it has zero/none!) or allow mixed read-write caching on Level2.
The problem I see are offline modifications. If other system writes to the same disk, after first system crashed with some write backlog in his Level2, that disk will have corrupted data, unwritten data left in Level2 cache. But, that is acceptable and won't occur to admins who are aware of it. Similar warning for corruption has every SAN storage when you create LUN disks: a warning the data will be corrupted it 2 systems write to it simultaneously.
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Re: bug or feature - direct L2 write cache without using L1 ram cache

Post by Support »

well, not that good...Even you only use L2 for defer-write, there still is the risk of data loss. We are still thinking about a solution to avoid this kind of risk.
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