Re: multiple journals on SSD

[Vincent Godin <vince.mlist@xxxxxxxxx>]

Hello.

I've been testing Intel 3500 as journal store for few HDD-based OSD. I
stumble on issues with multiple partitions (>4) and UDEV (sda5, sda6,etc
sometime do not appear after partition creation). And I'm thinking that
partition is not that useful for OSD management, because linux do no
allow partition rereading with it contains used volumes.

So my question: How you store many journals on SSD? My initial thoughts:

1)  filesystem with filebased journals
2) LVM with volumes

Anything else? Best practice?

P.S. I've done benchmarking: 3500 can support up to 16 10k-RPM HDD.

Hello,

I would like to advertise you not using 1 SSD for 16 HDD. Ceph journal is not only a journal but a write cache during operation. I had that kind of configuration with 1 SSD for 20  SATA HDD. With a Ceph bench, i notice that my rate whas limited between 350 and 400 MB/s. In fact, a iostat show me that my SSD was 100% utilised with a rate of 350-400 MB/s.

If you consider that a SATA HDD can have a max average rate of 100 MB/s, you need to configure one SSD (which can rate till 400 MB/s) for 4 SATA HDD

Vincent

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