Reduce bandwidth costs with dm-cache: fast local SSD caching for network storage

Re:Reduce bandwidth costs with dm-cache: fast local SSD cach... by mgerdts on Friday September 12, 2025 @11:29PM (#45229068)

I remember seeing another strategy where a remote block device was (lazily?) mirrored to a local SSD. The mirror was configured such that reads from the local device were preferred and writes would go to both devices. I think this was done by someone on GCP.

Does this ring any bells? I’ve searched for this a time or two and can’t find it again.

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Re:Reduce bandwidth costs with dm-cache: fast local SSD cach... by twotwotwo on Saturday September 13, 2025 @12:04AM (#45229214)

Discord: https://discord.com/blog/how-discord-supercharges-network-di...

(Somehow the name "SuperDisks" was burned into my brain for this. Although this post uses 'Super-Disks' in a title, if you search for SuperDisks you'll find pages about the LS-120 floppies that went by that name.)

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Re:Reduce bandwidth costs with dm-cache: fast local SSD cach... by cperciva on Saturday September 13, 2025 @12:01AM (#45229196)

I've done this on EC2 -- in particular back in the days when EBS billed per I/O (as opposed to using a "reserved IOPs" model where you say up front how much I/O performance you need). I haven't bothered recently since EBS performance is good enough for most purposes and there's no automatic cost savings.

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Re:Reduce bandwidth costs with dm-cache: fast local SSD cach... by zipmapfoldright on Saturday September 13, 2025 @04:50AM (#45230485)

Google's L4 cache? https://cloud.google.com/blog/products/storage-data-transfer...

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Re:Reduce bandwidth costs with dm-cache: fast local SSD cach... by magicalhippo on Saturday September 13, 2025 @07:34AM (#45231257)

There was some discussion amongst the ZFS devs for such a feature.

As I recall it was to change the current mirrored read strategy to be aware of the speed of the underlying devices, and prefer the faster if it has capacity. Though perhaps a fixed pool property to always read from a given device was discussed, it's been a while so my memory is hazy.

The use-case was similar IIRC, where a customer wanted to combine local SSD with remote block device.

So, might come to ZFS.

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