On 04/04/17 20:36, Peter Grandi wrote:
SATA works for external use, eSATA works well, but what really
matters is the chipset of the adapter card.
eSATA might be sound electrically, but mechanically it is awful. Try to
run it for months in a crowded server room, and inevitably you'll get
disconnections and data corruption. Tried different cables, brackets --
same result. If you ever used eSATA connector, you'd feel it.
In my experience JMicron is not so good, Marvell a bit better,
best is to use a recent motherboard chipset with a SATA-eSATA
internal cable and bracket.
That's exactly what I used to use: internal controller of Z77 chipset +
bracket(s).
But that does not change the fact that it is a library and work
is initiated by user requests which are not per-subvolume, but
in effect per-volume.
That's the answer I was looking for.
It is a way to do so and not a very good way. There is no
obviously good way to define "real usage" in the presence of
hard-links and reflinking, and qgroups use just one way to
define it. A similar problem happens with processes in the
presence of shared pages, multiple mapped shared libraries etc.
No need to over-generalize. There's an obvious good way to define "real
usage" of a subvolume and its snapshots as long as it don't share any
data with other subvolumes, as is often the case. If it does share, two
figures -- exclusive and referenced, like in qgroups -- are sufficient
for most tasks.
The problem is that
both hard-links and ref-linking create really significant
ambiguities as to used space. Plus the same problem would happen
with directories instead of subvolumes and hard-links instead of
reflinked snapshots.
You're right, although with hard-links there's at least remote chance to
estimate storage use with usermode scripts.
ASMedia USB3 chipsets are fairly reliable at the least the card
ones on the system side. The ones on the disk side I don't know
much about.
This is getting increasingly off-topic, but our mainstay are CFI 5-disk
DAS boxes (8253JDGG to be exact) filled with WD Red-s in RAID5
configuration. They are no longer produced and getting harder and harder
to source, but showed themselves as very reliable. According to lsusb
they contain JMicron JMS567 SATA 6Gb/s bridge.
--
With Best Regards,
Marat Khalili
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