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Is there an open source software available for Linux that implements a new block device based on an underlying block device (DRBD or shared SAN) and a distributed memory cache ?
What I'm looking for is something like memcached for block devices. This would be useful for VMs based on cluster LVM (clvmd), for instance.

Distributed means that each cached block is stored on only one of the nodes using that device such that the effective cache size is the sum of the cache sizes of the nodes. A block that is stored on one node and accessed from another node shall be forwarded on the network without accessing the underlying block device.

The cache should be write-through: Only reads should be cached, but writes should be saved (mirrored) in the cache in order to support subsequent reads.

Or should I better ask this question on software-recommendations ?

  • Have you looked at AFS/OpenAFS ? Seems the distributed network storage w/ strong client side caching would be what you want... – ivanivan Oct 18 '18 at 18:03
  • AFS is a file system. What I'm looking for is a block device. Do you think the overhead of using AFS to hold files below loopback devices is low enough to justify its use ? If you say yes, then I would go into an analysis of the AFS cache: Is it distributed in the sense that each cached block is stored on only one of the nodes and transported via the netowrk when needed elsewhere ? – Juergen Oct 19 '18 at 9:39

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