Explained: How LSI and Oracle cooked up magical flash-embiggening sauce
It’s all about compression, baby
Oracle and LSI have magicked up a way for LSI’s Nytro server flash cards to hold more data than they’re seemingly physically capable of holding and called it Dynamic Logical Capacity (DLC). How does it work?
We thought it might be a paging mechanism – but we were dead wrong. The card compresses the data it is sent and can reach a 2:1 compression ratio, depending on the data. With 50 per cent compression of the data, a 1TB Nytro card can hold 2TB of raw data.
This increases cache-hit rates and thereby increases server application performance. It reduces the cost/GB of the Nytro PCIe flash card storage and also the GB/watt measure. LSI says the compression is used for write amplification reduction as well as capacity extension.
The Nytro card reports its free space via an API, enabling the host system to send data up to the point its free capacity is used up. With the reporting OEMs can utilise DLC technology:
- APIs are used by host software to monitor usable Virtual Capacity
- It needs close coordination between the Nytro PCIe flash card and the application
- The application must monitor free flash space to maintain optimal performance and to guard against free flash space exhaustion.
LSI points out that the card’s logical space varies over time as the cached data’s compressibility changes.
El Reg’s storage desk was hit by a severe case of rear view recognition: Of course! Shouldn’t all flash cards be doing this? We expect they will. ®
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