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Re: Mixing HDD and SSD in lvm

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  Re: Mixing HDD and SSD in lvm Kamil Jońca <kjonca@o2.pl> - 2024-02-06 09:20 +0100
    Re: Mixing HDD and SSD in lvm Marco Moock <mm@dorfdsl.de> - 2024-02-06 09:30 +0100
      Re: Mixing HDD and SSD in lvm Basti <mailinglist@unix-solution.de> - 2024-02-06 11:50 +0100
        Re: Mixing HDD and SSD in lvm Andy Smith <andy@strugglers.net> - 2024-02-06 23:40 +0100

#267041 — Re: Mixing HDD and SSD in lvm

Marco Moock <mm@dorfdsl.de> writes:

> Am 06.02.2024 um 07:17:02 Uhr schrieb Kamil Jońca:
>
>> Should I worry about anything (speed differences or sth)?
>
> Speed differences will occur because reading and writing from/to the
> SSD will be much faster.
Of course, but can it make any data damage to lvm?

I am asking because some time ago was a (different) story  about SMR
drives whose can make problem when in RAID. And I am wondering if here I
can similar problems.

KJ

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#267042

Am 06.02.2024 um 08:54:18 Uhr schrieb Kamil Jońca:

> Marco Moock <mm@dorfdsl.de> writes:
> 
> > Am 06.02.2024 um 07:17:02 Uhr schrieb Kamil Jońca:
> >  
> >> Should I worry about anything (speed differences or sth)?  
> >
> > Speed differences will occur because reading and writing from/to the
> > SSD will be much faster.  
> Of course, but can it make any data damage to lvm?
> 
> I am asking because some time ago was a (different) story  about SMR
> drives whose can make problem when in RAID. And I am wondering if
> here I can similar problems.

That was because they have a significant decrease in writing
performance when shingled data needs to be rewritten.
Some RAID controllers treated that as a drive failure.
SSDs normally have a constant write speed, so I don't think this
problem occurs here.

-- 
Gruß
Marco

Spam und Werbung bitte an ichschickereklame@cartoonies.org

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#267049

If you use mdadm for RAID you can mark the slower disk as 'write-mostly' 
to get more read speed.

On 06.02.24 09:23, Marco Moock wrote:
> Am 06.02.2024 um 08:54:18 Uhr schrieb Kamil Jońca:
>
>> Marco Moock <mm@dorfdsl.de> writes:
>>
>>> Am 06.02.2024 um 07:17:02 Uhr schrieb Kamil Jońca:
>>>   
>>>> Should I worry about anything (speed differences or sth)?
>>> Speed differences will occur because reading and writing from/to the
>>> SSD will be much faster.
>> Of course, but can it make any data damage to lvm?
>>
>> I am asking because some time ago was a (different) story  about SMR
>> drives whose can make problem when in RAID. And I am wondering if
>> here I can similar problems.
> That was because they have a significant decrease in writing
> performance when shingled data needs to be rewritten.
> Some RAID controllers treated that as a drive failure.
> SSDs normally have a constant write speed, so I don't think this
> problem occurs here.
>

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#267091

Hi,

On Tue, Feb 06, 2024 at 11:03:03AM +0100, Basti wrote:
> If you use mdadm for RAID you can mark the slower disk as 'write-mostly' to
> get more read speed.

Both (MD) RAID-1 and RAID-10 will work this out by themselves, by
the way, and tend to read from the fastest device.

I have benchmarked this. With very fast enterprise NVMe as the
faster device and consumer SATA SSD as the slower "write-mostly", I
wasn't able to detect much benefit from using "write-mostly", i.e.
MD already chose to read mostly from the NVMe.

When pairing any kind of SSD with HDD, the difference was more
dramatic and "write-mostly" did have noticeable beneficial effect,
though not huge. Again, MD by itself chose to read from the SSD even
without "write-mostly".

I hypothesise that this is because MD picks the mirror device with
the lowest outstanding request count, and that is often going to be
the flash-based device.

Thanks,
Andy

-- 
https://bitfolk.com/ -- No-nonsense VPS hosting

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