On Fri, September 8, 2017 11:07 am, Stephen John Smoogen wrote:
> On 8 September 2017 at 11:00, Valeri Galtsev <galtsev@xxxxxxxxxxxxxxxxx>
> wrote:
>>
>> On Fri, September 8, 2017 9:48 am, hw wrote:
>>> m.roth@xxxxxxxxx wrote:
>>>> hw wrote:
>>>>> Mark Haney wrote:
>>>> <snip>
>>>>>> BTRFS isn't going to impact I/O any more significantly than, say,
>>>>>> XFS.
>>>>>
>>>>> But mdadm does, the impact is severe. I know there are ppl saying
>>>>> otherwise, but I�´ve seen the impact myself, and I definitely
>>>>> don�´t
>>>>> want
>>>>> it on that particular server because it would likely interfere with
>>>>> other services.
>>>> <snip>
>>>> I haven't really been following this thread, but if your requirements
>>>> are
>>>> that heavy, you're past the point that you need to spring some money
>>>> and
>>>> buy hardware RAID cards, like LSI, er, Avago, I mean, who's bought
>>>> them
>>>> more recently?
>>>
>>> Heavy requirements are not required for the impact of md-RAID to be
>>> noticeable.
>>>
>>> Hardware RAID is already in place, but the SSDs are "extra" and, as I
>>> said,
>>> not suited to be used with hardware RAID.
>>
>> Could someone, please, elaborate on the statement that "SSDs are not
>> suitable for hardware RAID".
>>
>
> It will depend on the type of SSD and the type of hardware RAID. There
> are at least 4 different classes of SSD drives with different levels
> of cache, write/read performance, number of lifetime writes, etc.
> There are also multiple types of hardware RAID. A lot of hardware RAID
> will try to even out disk usage in different ways. This means 'moving'
> the heavily used data from slow parts to fast parts etc etc.
Wow, you learn something every day ;-) Which hardware RAIDs do these
moving of data (manufacturer/model, please - believe it or not I never
heard of that ;-). And "slow part" and "fast part" of what are data being
moved between?
Thanks in advance for tutorial!
Valeri
> On an SSD
> all these extra writes aren't needed and so if the hardware RAID
> doesn't know about SSD technology it will wear out the SSD quickly.
> Other hardware raid parts that can cause faster failures on SSD's are
> where it does test writes all the time to see if disks are bad etc.
> Again if you have gone with commodity SSD's this will wear out the
> drive faster than expected and boom bad disks.
>
> That said, some hardware RAID's are supposedly made to work with SSD
> drive technology. They don't do those extra writes, they also assume
> that the disks underneath will read/write in near constant time so
> queueing of data is done differently. However that stuff costs extra
> money and not usually shipped in standard OEM hardware.
>
>
>> Thanks.
>> Valeri
>>
>>>
>>> It remains to be tested how the hardware RAID performs, which may be
>>> even
>>> better than the SSDs.
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>>
>>
>> ++++++++++++++++++++++++++++++++++++++++
>> Valeri Galtsev
>> Sr System Administrator
>> Department of Astronomy and Astrophysics
>> Kavli Institute for Cosmological Physics
>> University of Chicago
>> Phone: 773-702-4247
>> ++++++++++++++++++++++++++++++++++++++++
>> _______________________________________________
>> CentOS mailing list
>> CentOS@xxxxxxxxxx
>> https://lists.centos.org/mailman/listinfo/centos
>
>
>
> --
> Stephen J Smoogen.
> _______________________________________________
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> https://lists.centos.org/mailman/listinfo/centos
>
++++++++++++++++++++++++++++++++++++++++
Valeri Galtsev
Sr System Administrator
Department of Astronomy and Astrophysics
Kavli Institute for Cosmological Physics
University of Chicago
Phone: 773-702-4247
++++++++++++++++++++++++++++++++++++++++
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