109 is 81.75 yes the rest of them some bluestore stuffs I guess. Istvan Szabo Senior Infrastructure Engineer --------------------------------------------------- Agoda Services Co., Ltd. e: istvan.szabo(a)agoda.com --------------------------------------------------- -----Original Message----- From: Simon Sutter <ssutter(a)hosttech.ch> Sent: Thursday, February 25, 2021 5:55 PM To: ceph-users(a)ceph.io Subject: [ceph-users] Erasure coded calculation Email received from outside the company. If in doubt don't click links nor open attachments! ________________________________ Hello everyone! I'm trying to calculate the theoretical usable storage of a ceph cluster with erasure coded pools. I have 8 nodes and the profile for all data pools will be k=6 m=2. If every node has 6 x 1TB wouldn't the calculation be like this: RAW capacity: 8Nodes x 6Disks x 1TB = 48TB Loss to m=2: 48TB / 8Nodes x 2m = 12TB EC capacity: 48TB - 12TB = 36TB At the moment I have one cluster with 8 nodes and different disks than the sample (but every node has the same amount of disks and the same sized disks). The output of ceph df detail is: --- RAW STORAGE --- CLASS SIZE AVAIL USED RAW USED %RAW USED hdd 109 TiB 103 TiB 5.8 TiB 5.9 TiB 5.41 TOTAL 109 TiB 103 TiB 5.8 TiB 5.9 TiB 5.41 --- POOLS --- POOL ID PGS STORED OBJECTS %USED MAX AVAIL device_health_metrics 1 1 51 MiB 48 0 30 TiB rep_data_fs 2 32 14 KiB 3.41k 0 30 TiB rep_meta_fs 3 32 227 MiB 1.72k 0 30 TiB ec_bkp1 4 32 4.2 TiB 1.10M 6.11 67 TiB So ec_bkp1 uses 4.2TiB an there are 67TiB free usable Storage. This means total EC usable storage would be 71.2TiB. But calculating with the 109TiB RAW storage, shouldn't it be 81.75? Are the 10TiB just some overhead (that would be much overhead) or is the calculation not correct? And what If I want to expand the cluster in the first sample above by three nodes with 6 x 2TB, which means not the same sized disks as the others. Will the calculation with the same EC profile still be the same? RAW capacity: 8Nodes x 6Disks x 1TB + 3Nodes x 6Disks x 2TB = 84TB Loss to m=2: 84TB / 11Nodes x 2m = 15.27TB EC capacity: 84TB - 15.27TB = 68.72TB Thanks in advance, Simon _______________________________________________ ceph-users mailing list -- ceph-users(a)ceph.io To unsubscribe send an email to ceph-users-leave(a)ceph.io ________________________________ This message is confidential and is for the sole use of the intended recipient(s). It may also be privileged or otherwise protected by copyright or other legal rules. If you have received it by mistake please let us know by reply email and delete it from your system. It is prohibited to copy this message or disclose its content to anyone. Any confidentiality or privilege is not waived or lost by any mistaken delivery or unauthorized disclosure of the message. All messages sent to and from Agoda may be monitored to ensure compliance with company policies, to protect the company's interests and to remove potential malware. Electronic messages may be intercepted, amended, lost or deleted, or contain viruses.