Re: Poor raid 1 performance?

"Antoine Leca" <root@xxxxxxxxxxxxxxxxx> wrote in message news:439089e4$0$21227$626a54ce@xxxxxxxxxxxx
> In news:2xpj4ixtna3d.63e6kmv1z3h9$.dlg@xxxxxxxxxx, Gerhard Fiedler va escriure:
> > Peter wrote:
> >
> > > It is organized very differently. There are NO STRIPES in RAID1. On
> > > each disk data seem to be organized exactly the same as on
> > > standalone hard drive.
> >
> > Of course there are no RAID0 stripes in RAID1. But for reading, a
> > stripe is nothing more than a subset of data.
>
> The difference between RAID 0 and RAID 1 is the distance between one stripe
> and the next on disk. With RAID 0, they are contiguous for both reading and
> writing. With RAID 1, you cannot make them contiguous or near enough for
> both writing [every sector] and reading [every two sectors].

So that's obviously not the way to do it.

>
> So the obvious organisation is to make OK for writing (so just like a normal disk),

> and while sequential reading you should wait while
> skipping the odd-numbered sector which is in between.

That's silly.
You divide a single request into two and send each half to a different drive.
With consequtive requests (for a sequential file) you sent half the number of
total requests to one drive and the other half to the other one, resulting in
both drives reading sequentially.

>
> There is a gain though (half traffic on the wire, for example),

That's not a perceptive gain.

> but I guess media access is the bottleneck.
>
>
> Antoine
.

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