[notepad] ceph journal size/ssd speed

ceph journal size (doc)

osd journal size = {2 * (expected throughput * filestore max sync interval)}

The default for filestore max sync interval is 5 therefore for a 10Gbit network the “perfect” size would be

osd journal size = { 2 * ( 1280 * 5 ) } = 12.5 GB

ceph ssd speed (journal)

The optimum would be sum of all disk seq write speeds – 11 disks with ~110mb/s = ~1210mb/s – an Intel P3520 might would fit.

How many journals per ssd?

Oh thats easy.

Journals = (ssd seq write speed) / (hdd seq write speed)

Journals = 1350 / 115 = ~11

(For the Intel P3520 with 11 hdds)

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