Re: [PATCH 0/4] 3- and 4- copy RAID1

From: "Austin S. Hemmelgarn" <ahferroin7@gmail.com>
To: Hugo Mills <hugo@carfax.org.uk>,
	Andrei Borzenkov <arvidjaar@gmail.com>,
	kreijack@inwind.it, Duncan <1i5t5.duncan@cox.net>,
	linux-btrfs@vger.kernel.org
Subject: Re: [PATCH 0/4] 3- and 4- copy RAID1
Date: Fri, 20 Jul 2018 14:46:42 -0400	[thread overview]
Message-ID: <ac9b68aa-0d4c-1d8c-9a5c-a5d9dda7473c@gmail.com> (raw)
In-Reply-To: <20180720184159.GD21293@carfax.org.uk>

On 2018-07-20 14:41, Hugo Mills wrote:
> On Fri, Jul 20, 2018 at 09:38:14PM +0300, Andrei Borzenkov wrote:
>> 20.07.2018 20:16, Goffredo Baroncelli пишет:
> [snip]
>>> Limiting the number of disk per raid, in BTRFS would be quite simple to implement in the "chunk allocator"
>>>
>>
>> You mean that currently RAID5 stripe size is equal to number of disks?
>> Well, I suppose nobody is using btrfs with disk pools of two or three
>> digits size.
> 
>     But they are (even if not very many of them) -- we've seen at least
> one person with something like 40 or 50 devices in the array. They'd
> definitely got into /dev/sdac territory. I don't recall what RAID level
> they were using. I think it was either RAID-1 or -10.
> 
>     That's the largest I can recall seeing mention of, though.
I've talked to at least two people using it on 100+ disks in a SAN 
situation.  In both cases however, BTRFS itself was only seeing about 20 
devices and running in raid0 mode on them, with each of those being a 
RAID6 volume configured on the SAN node holding the disks for it.  From 
what I understood when talking to them, they actually got rather good 
performance in this setup, though maintenance was a bit of a pain.