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I have Debian based Openmediavault 3.0 distribution with iscsi plugin based on ietd. Among others, I use it to serve several disks as ISCSI block mode for VMWare servers. It works, however it is getting out of IOPs slowly.

I wanted to add SSD to cache read/write operations.Best if it will provide caching for several disks on single SSD. Unfortunately, I found that open source caching require somehow preparing disks before use and it not working with unmodified RAW storage I have. I cant prepare disks because these disks are VMFS formatted and planned to put back in the server if no caching method will be found.

I wonder if it is possible at all. I can change ISCSI software if needed.

Thanks.

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  • Basically, you have replied to your question: prepare somehow disks to check SSD cache functionality.
    – Mr. Raspberry
    Apr 3, 2017 at 17:17
  • This is probably not something that iSCSI itself provides - but the underlying storage that is being served. If you configure your storageserver to utilize SSD-caching (or atleast the partition/block you are sharing) - the target till have SSD-caching-functionality
    – Orphans
    Jan 25, 2022 at 9:50

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There are a number of tools for block caching, for example bcache, dm-cache, and enhanceio. Keep in mind that write-caching trades off durability for speed; if there is an error writing to the backing disk, executing programs are well past the point where they can receive the error message.

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    This! That's why almost all storage vendors are using Write-through mode of SSD cache. So instead of increasing underlying storage with SSD, it would be better to create an iSCSI target on top of underlying storage and use it for performance hungry applications.
    – Stuka
    Apr 3, 2017 at 14:13

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