On 2017-09-21 10:01, Dietmar Rieder wrote:
> Hi,
>
> I'm in the same situation (NVMEs, SSDs, SAS HDDs). I asked the same
> questions to myself.
> For now I decided to use the NVMEs as wal and db devices for the SAS
> HDDs and on the SSDs I colocate wal and db.
>
> However, I'm still wonderin how (to what size) and if I should change
> the default sizes of wal and db.
>
> Dietmar
>
> On 09/21/2017 01:18 AM, Alejandro Comisario wrote:
>
>> But for example, on the same server i have 3 disks technologies to
>> deploy pools, SSD, SAS and SATA.
>> The NVME were bought just thinking on the journal for SATA and SAS,
>> since journals for SSD were colocated.
>>
>> But now, exactly the same scenario, should i trust the NVME for the SSD
>> pool ? are there that much of a gain ? against colocating block.* on
>> the same SSD?
>>
>> best.
>>
>> On Wed, Sep 20, 2017 at 6:36 PM, Nigel Williams
>> <[email protected] <mailto:[email protected]>> wrote:
>>
>> On 21 September 2017 at 04:53, Maximiliano Venesio
>> <[email protected] <mailto:[email protected]>> wrote:
>>
>> Hi guys i'm reading different documents about bluestore, and it
>> never recommends to use NVRAM to store the bluefs db,
>> nevertheless the official documentation says that, is better to
>> use the faster device to put the block.db in.
>>
>> Likely not mentioned since no one yet has had the opportunity to
>> test it.
>>
>> So how do i have to deploy using bluestore, regarding where i
>> should put block.wal and block.db ?
>>
>> block.* would be best on your NVRAM device, like this:
>>
>> ceph-deploy osd create --bluestore c0osd-136:/dev/sda --block-wal
>> /dev/nvme0n1 --block-db /dev/nvme0n1
>>
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>> *CTO | NUBELIU*
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My guess is for wal: you are dealing with a 2 step io operation so in
case it is collocated on your SSDs your iops for small writes will be
halfed. The decision is if you add a small NVMEs as wal for 4 or 5
(large) SSDs, you will double their iops for small io sized. This is not
the case for db.
For wal size: 512 MB is recommended ( ceph-disk default )
For db size: a "few" GB..probably 10GB is a good number. I guess we will
hear more in the future.
Maged Mokhtar
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