[dilyevsky]

> So if you pay for 1GB of storage, they probably actually store 5GB of data or more for you

The actual factor is most likely around 1.4-1.5x and for sure can’t be any more than 2.2x in this day and age. Dumbest possible implementation will be “only” 3x so no it’s nowhere close to 5gb

Edit: looks like it’s public so i can actually tell you that google uses RS 3,2 which gives 1.5 replication factor. When i was there a few years ago storage folks told me they never lost a single stripe of data

[pclmulqdq]

Those numbers are for Colossus. Blobstore, which backs the cloud object store, is different, and used to be a lot higher.

[dilyevsky]

Yeah those aren’t public afaik, iirc they adjusted replication for cold data

[teraflop]

Presumably Google also keeps backups, though, right?

[dietr1ch]

And mirrors to at least one extra datacenter as they can lose bandwidth with a fiber getting cut, become unreachable due to networking snafu, or even burn down entirely.

[dilyevsky]

Yes they also store to tape

[AuthorizedCust]

That means 2X at a minimum. Then RAID overhead. Possibly other hot or warm copies ready to take over instantly.

[dilyevsky]

And tape costs same as ssd/spindles in your calculations?

[pests]

A common problem would be throughput though. Storage capacity scales much faster than access speed. If you are storing an item only 3 times and lets say each storage location gives you 50,000 IOPS max then you can only ever service 150,000 IOPS of this item which might not be enough.

[dilyevsky]

Vast majority of data rarely (if ever) gets read so you use a cache for that

[killingtime74]

What does RS 3,2 stand for? Thanks

[dilyevsky]

Reed-Solomon erasure coding. 2 data blocks, one parity. Basically raid-6 but distributed

[londons_explore]

But thats within one cell... But data will be stored in more than one cell to deal with scheduled and unscheduled downtime of the cell...

[dilyevsky]

You have pay more for that

[smueller1234]

Not with GCS, you don't.

https://cloud.google.com/storage/docs/availability-durabilit...

Are you thinking of Persistent Disk (PD) and Replicated PD?

(I work on storage at Google.)

[dilyevsky]

I was thinking of gcp regions in which case you do have to pay for it. For colossus cells within a single regions you obviously don't but I don't know enough how it maps it out down there and whether it just moves data around in the event of PCR