Re: Raid 1 recovery from HD failure

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Phillip Windell <philwindell@xxxxxxxxxxx> wrote:

Since it is RAID1 there is no performance loss with running only one
drive. Although there may be a little during the rebuild. It is the
Striped-Sets with Pairity (RAID5) that loose performance with a dead
drive.

I was under the impression that the better RAID-1 controllers could do
reads in a fashion similar to RAID-0 reads, where different sectors from
each disk are read at the same time, for the same file.

1 and 0 work completely differently

"RAID 0" just joins the disk "end-to-end" figuratively speaking. One
disk is not a "copy" of the other disk,...so the file does not exist on
both drives,...it will be either on one drive or the other or may be
half on one drive and half on the other. If one drive dies the whole
thing is lost,..there is no fault tolerance.

Thanks, but I know how RAID-0 works. I have worked with people in one of
the very few fields that can make effective use of RAID-0 (video editing).


But with "RAID 1" each disk is a complete copy of the other. So I don't
see how the file access could be done the same way with each type.

You should have read what I said properly, as you know how RAID-0 works.

In RAID-1 the disks are mirrored, so, the controller can read different
sectors from each disk at the same time, increasing performance. The
effective performance can actually be greater than RAID-0's (in the more
common scenario of dealing with lots of small files, like in an operating
system) as the disks' access time is theoretically halved, where in RAID-0
is it the same as a single disk (which is the big reason RAID-0 is pretty
useless for everyday situations).


But I'm not going to claim to know how all the different hardware vendors
choose implement their stuff.

Since it is RAID1 there is no performance loss with running only one
drive.

Read the first paragraph of this section of the page:

http://en.wikipedia.org/wiki/Standard_RAID_levels#RAID_1_performance

ss.


.

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