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ceph SSD journaling on same drive

asked 2017-03-24 14:22:38 -0500

Damian Dąbrowski gravatar image

updated 2017-03-24 14:25:36 -0500

Hello,

In my enviroment I'll use 3 hosts * 6 SSD OSD each. I wonder what will be better for me:

a) buy 128GB SSD NVMe disk(I see here such disadvantages as eg. lack of possibility to hot-swap disk when it fail)

b) place 10GB partition on each SSD for journaling

What do You think? Which option will be better? Documentation says that dedicated disk for journal is pretty good idea, but I've heard opinions that on SSD OSD's there is no need to use dedicated disk for journaling.

Thanks for the answers.

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answered 2017-05-26 13:02:29 -0500

bene gravatar image

Even SATA/SAS SSDs are much slower than NVM SSDs, and some of them are not much better than HDDs at doing journaling writes, which are sequential, very small requests, and have to be committed to persistent storage immediately. Some NVM SSDs can do journaling writes 1-2 orders of magnitude faster than SATA/SAS SSDs. So I could see using an NVM SSD as an SSD journal for SATA/SAS OSDs. However, if you have many SATA/SAS SSDs per host (e.g. > 10), I'm guessing that you might be better off with co-located journals since at that point the NVM SSD may be more likely to become a bottleneck, depending on the workload.

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Thank You, That's great answer.

Damian Dąbrowski gravatar imageDamian Dąbrowski ( 2017-06-07 03:48:16 -0500 )edit

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Asked: 2017-03-24 14:22:38 -0500

Seen: 239 times

Last updated: Mar 24 '17