Re: RAID-1 - suboptimal write performance?

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On Fri, 2014-05-16 at 16:48 +0100, Tomasz Chmielewski wrote:
> While doing rsyncs of large archives from one RAID-1 btrfs filesystem
> to another RAID-1 btrfs filesystem:
> 
> btrfs filesystem 1: sda + sdb (RAID-1), being copied to:
> btrfs filesystem 2: sdc + sdd (RAID-1)
> Server has 32 GB RAM
> 
> 
> I can observe the following:
> 
> 
> From time to time, rsync "freezes", while there is high IO on only *one*
> of write drives.

No comment on the performance issue, other than to say that I've seen
similar on RAID-10 before, I think.

> Also, what happens when the system crashes, and one drive has several
> hundred megabytes data more than the other one?

This shouldn't be an issue as long as you occasionally run a scrub or
balance. The scrub should find it and fix the missing data, and a
balance would just rewrite it as proper RAID-1 as a matter of course.

-- 
Calvin Walton <calvin.walton@xxxxxxxxxx>

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