On 2013-08-24 14:30, Sandy McArthur wrote:
I was surprised to find
that I'm not allowed to remove one of the two drives in a RAID1. Kernel
message is "btrfs: unable to go below two devices on raid1" Not
allowing it
by default makes some sense, however a --force flag or something would
be
beneficial.
If you have an USB enclosure you could connect another drive via USB
temporarily.
That said my biggest btrfs problem happened while I had some drives on
SATA and others on USB.
Ah, indeed, a close look at my device names reveals that I claim to only
have three SATA ports, but sdc and sdd are used for my btrfs test. The
sdb device is in fact an external USB enclosure that I'm using as my
data source for the testing.
I'm really just wanting to test what I see as some common use cases for
a RAID1 btrfs filesystem. A very common one that seems to fail currently
is wishing to preemptively (SMART errors on drive, many other reasons)
remove it from the mirror, in order to add a replacement device - and
keep things online during the entire process. As I see it now, I'd need
to umount, forcibly/uncleanly pull the drive, mount degraded, add the
new device, umount, mount cleanly, rebalance and move forward.
I'd like to use btrfs for the data checksumming, however based on my
investigations it doesn't appear to be ready for the set of RAID1
support I'd expect. Based on that, I'm relooking at options.
Are there any known gotchas or limitations with a btrfs filesystem with
single data and metadata, running on top of an md-raid RAID1 mirror?
Joel
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