Re: Hardware recommendations

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От Arjen van der Meijden
Тема Re: Hardware recommendations
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Msg-id 4D026A09.3080108@tweakers.net
обсуждение исходный текст
Ответ на Re: Hardware recommendations  (Andy)
Ответы Re: Hardware recommendations  (Arjen van der Meijden)
Re: Hardware recommendations  (Andy)
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Hardware recommendations  ("Benjamin Krajmalnik", )
 Re: Hardware recommendations  (Andy, )
  Re: Hardware recommendations  (Marti Raudsepp, )
   Re: Hardware recommendations  (Andy, )
    Re: Hardware recommendations  ("mark", )
 Re: Hardware recommendations  (, )
 Re: Hardware recommendations  ("Benjamin Krajmalnik", )
  Re: Hardware recommendations  (Scott Marlowe, )
   Re: Hardware recommendations  (Marti Raudsepp, )
    Re: Hardware recommendations  (John W Strange, )
 Re: Hardware recommendations  (John W Strange, )
  Re: Hardware recommendations  (Greg Smith, )
 Re: Hardware recommendations  (, )
 Re: Hardware recommendations  (, )
 Re: Hardware recommendations  (, )
 Re: Hardware recommendations  (, )
 Re: Hardware recommendations  (, )
 Re: Hardware recommendations  (alan bryan, )
  Re: Hardware recommendations  (Andy, )
   Re: Hardware recommendations  (Arjen van der Meijden, )
    Re: Hardware recommendations  (Arjen van der Meijden, )
     Re: Hardware recommendations  (Scott Marlowe, )
    Re: Hardware recommendations  (Andy, )
 Re: Hardware recommendations  (Greg Smith, )
  Re: Hardware recommendations  ("Benjamin Krajmalnik", )
   Re: Hardware recommendations  ("mark", )
On 10-12-2010 14:58 Andy wrote:
>> We use ZFS and use SSDs for both the log device and L2ARC.  All
>> disks and SSDs are behind a 3ware with BBU in single disk mode.
>
> Out of curiosity why do you put your log on SSD? Log is all
> sequential IOs, an area in which SSD is not any faster than HDD. So
> I'd think putting log on SSD wouldn't give you any performance
> boost.

The "common knowledge" you based that comment on, may actually not be
very up-to-date anymore. Current consumer-grade SSD's can achieve up to
200MB/sec when writing sequentially and they can probably do that a lot
more consistent than a hard disk.

Have a look here: http://www.anandtech.com/show/2829/21
The sequential writes-graphs consistently put several SSD's at twice the
performance of the VelociRaptor 300GB 10k rpm disk and that's a test
from over a year old, current SSD's have increased in performance,
whereas I'm not so sure there was much improvement in platter based
disks lately?

Apart from that, I'd guess that log-devices benefit from reduced latencies.

Its actually the recommended approach from Sun to add a pair of (small
SLC-based) ssd log devices to increase performance (especially for
nfs-scenario's where a lot of synchonous writes occur) and they offer it
as an option for most of their "Unified Storage" appliances.

Best regards,

Arjen

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