On 16/06/2020 12:26, Dale wrote:
I've also read about the resilvering problems too. I think LVM
snapshots and something about BTFS(sp?) has problems. I've also read
that on windoze, it can cause a system to freeze while it is trying to
rewrite the moved data too. It gets so slow, it actually makes the OS
not respond. I suspect it could happen on Linux to if the conditions
are right.
Being all technical, what seems to be happening is ...
Random writes fillup the PMR cache. The drive starts flushing the cache,
but unfortunately you need a doubly linked list or something - you need
to be able to find the physical block from the logical address (for
reading) and to find the logical block from the physical address (for
cache-flushing). So once the cache fills, the drive needs "down time" to
move stuff around, and it stops responding to the bus. There are reports
of disk stalls of 10 minutes or more - bear in mind desktop drives are
classed as unsuitable for raid because they stall for *up* *to* *two*
minutes ...
I guess this is about saving money for the drive makers. The part that
seems to really get under peoples skin tho, them putting those drives
out there without telling people that they made changes that affect
performance. It's bad enough for people who use them where they work
well but the people that use RAID and such, it seems to bring them to
their knees at times. I can't count the number of times I've read that
people support a class action lawsuit over shipping SMR without telling
anyone. It could happen and I'm not sure it shouldn't. People using
RAID and such, especially in some systems, they need performance not
drives that beat themselves to death.
Most manufacturers haven't been open, but at least - apart from WD -
they haven't been stupid either. Bear in mind WD actively market their
Red drives as suitable for NAS or Raid, putting SMR in there was
absolutely dumb. Certainly in the UK, as soon as news starts getting
round, they'll probably find themselves (or rather their retailers will
get shafted with) loads of returns as "unfit for purpose". And,
basically, they have a legal liability with no leg to stand on because
if a product doesn't do what it's advertised for, then the customer is
*entitled* to a refund.
Dunno why, I've never been a WD fan, so I dodged that bullet. I just
caught another one, because I regularly advise people they shouldn't be
running Barracudas, while running two myself ... :-)
Cheers,
Wol
