# [OmniOS-discuss] 4kn or 512e with ashift=12

Fred Liu Fred_Liu at issi.com
Tue Mar 22 10:21:19 UTC 2016

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    > -----Original Message-----
    > From: OmniOS-discuss [mailto:omnios-discuss-bounces at lists.omniti.com] On
    > Behalf Of Richard Elling
    > Sent: 星期二, 三月 22, 2016 3:19
    > To: Richard Jahnel
    > Cc: omnios-discuss at lists.omniti.com
    > Subject: Re: [OmniOS-discuss] 4kn or 512e with ashift=12
    >
    >
    > > On Mar 21, 2016, at 12:00 PM, Richard Jahnel <rjahnel at ellipseinc.com>
    > wrote:
    > >
    > > Both approaches have their error points.
    > >
    > > FWIW I would very very much like to be able to force my new pools into
    > ashift=12. It would make drive purchasing and replacement a lot more straight
    > forward and future resistant.
    >
    > The fundamental problem is that this is a vdev-settable, not a pool settable.
    > Today, it is very common for pools to have multiple ashifts active. Recently,
    > per-vdev ZAP objects have been proposed and that code is working its way
    > through the review and integration process.

    Not sure how multiple-ashifts impact the performace.
    >
    > Meanwhile, use one or more of the dozens of methods documented for doing
    > this.
    >
    > FWIW, most people with HDDs want space efficiency, because HDDs lost the
    > performance race to SSDs long ago. In general, forcing everything to 4k reduces
    > space efficiency, so it is unlikely to be a good default.

    Agree.

    Thanks.

    Fred

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