Hi, > Is it possible to recover two data chunks out of 2 coding chunks? Yes. > What do you think about 2+4, is it a good idea or a bad one? Some differences between a replica pool and an erasure code pool to consider: 1. If an OSD fails there will be a lot more network traffic between the sites to backfill/recover an erasure coded pool than a replica pool. 2. Replica pools can be configured to support local reads where clients send read I/O requests to an OSD at the same site. For erasure coded pools all read I/O must be sent via the primary OSD which half the time will be on the remote site. 3. In general, there will be more inter-site traffic with an erasure code pool than a replica pool. If the round trip latency between sites is really low and you have plenty of network bandwidth this might not be an issue, otherwise this will impact performance. Cheers, Bill. bill_scales@xxxxxxxxxx<mailto:bill_scales@xxxxxxxxxx> IBM Distinguished Engineer, IBM Storage From: Andre Tann <atann@xxxxxxxxxxxx> Date: Thursday, 10 October 2024 at 00:16 To: ceph-users@xxxxxxx <ceph-users@xxxxxxx> Subject: [EXTERNAL] Erasure coding scheme 2+4 = good idea? Hi all, I'd like your thoughts and comments on this idea: Setup: - two fault domains = DCs - connected with 100 GBit, < 1 ms - 80 NVME SSDs on each side Goal: One fault domain can be lost, and then there's still have some redundancy. Option 1: Replicated pool with size = 4. This gives me two copies on each side, thus meets the goal. But the efficiency is only 25%. Option 2: Erasure coded pool with 2 + 4 scheme. This gives me 3 chunks on each side. If I lose one side, I still have 3 chunks left, where I only need 2. Thus the goal is also met. Efficiency is 33%. Even though I did a lot of googling, I couldn't find anything about a similar setup. In all profiles, there is k <= m. What do you think about 2+4, is it a good idea or a bad one, or do I miss something and it doesn't work at all? In particular: is it possible to recover two data chunks out of 2 coding chunks? As I read the documentation, this should be no problem, just want to confirm. -- Andre Tann _______________________________________________ ceph-users mailing list -- ceph-users@xxxxxxx To unsubscribe send an email to ceph-users-leave@xxxxxxx Unless otherwise stated above: IBM United Kingdom Limited Registered in England and Wales with number 741598 Registered office: Building C, IBM Hursley Office, Hursley Park Road, Winchester, Hampshire SO21 2JN _______________________________________________ ceph-users mailing list -- ceph-users@xxxxxxx To unsubscribe send an email to ceph-users-leave@xxxxxxx
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