On 9/10/20 8:34 AM, heming.zhao wrote:
On 9/10/20 1:17 AM, Zdenek Kabelac wrote:
Dne 09. 09. 20 v 18:47 Zhao Heming napsal(a):
report LV is usable for upper layer.
leave issues
- this patch doesn't contain dm table comparison. So if the disk
is removed then re-inserted, but the re-inserted disk
major:minor is changed, the code doesn't have ability to detect.
- raid10: removing any 2 disks will think as array broken.
Signed-off-by: Zhao Heming <heming.zhao@xxxxxxxx>
---
v2:
- remove dm table parsing code in _lv_is_usable()
- add new status bit NOT_USABLE_LV.
note, I chose the first available bit 0x0000000080000000
- _lvusable_disp() uses lv_is_usable() to return usable status
dm_list_iterate_items(lvseg, &lv->segments) {
for (s = 0; s < lvseg->area_count; ++s) {
if (seg_type(lvseg, s) == AREA_PV) {
- if (is_missing_pv(seg_pv(lvseg, s)))
+ pv = seg_pv(lvseg, s);
+ if (!(pv->dev) && is_missing_pv(pv)) {
lv->status |= PARTIAL_LV;
+ lv->status |= NOT_USABLE_LV;
+ }
}
}
}
Hi
As it can be seen here - there is big intersection with meaning of
PARTIAL_LV.
The semantics of a usable LV is fuzzy by definition, because for
instance a multi-segment PARTIAL_LV
linear LV with a subset if its segments missing is still accessible
relative to the remaining segments
thus doesn't make it unusable. As a result, LVs failing t o activate
would be the 'unusable ones'.
The later is given for RAID when it's, e.g. missing more than its
maximum number of parity devices
for striped RAID layouts. So PARTIAL_LV is sufficient to tell that any
LV is still partially usable.
And the question is - what does it mean in the context of various
segment
types.
I believe we need to discuss with Heinz - whether we want to mark
Raid LVs partial in case they are actually 'only leg-pertial' and should
be actually activatable without partial activation - which is ATM
abused for this purpose.
Degraded RAID layouts are always usable unless more than its parity
devices or all its mirrors failed because of missing PVs. Hence such
activatable RaidLVs are not partial at the LV but at the SubLV Level.
ATM I'm not sure we want to introduce new flags, which has only slight
deviation from current partial flag - which should deserve closer look
of its meaning.
We'll try to find something with Heinz to agree with.
Ok, wait for feedback from Heinz.
What are we missing if we define any SubLV partial state with
PARTIAL_LV/not activatable and
leave it to the specific segment type handlers of the mappings on top of
such SubLVs
to define their respective PARTIAL_LV state or reject activation. E.g. a
fully usable RAID6 with a maximimum of 2 missing legs with those missing
legs either being partial and RAID6 I/O addressing a missing segment
-or- thise leg SubLVs not having been activated _not_ setting PATIAL_LV
on the RAID6 LV ('lvs -oname,attr,devices' will show state details on
the LV tree nodes).
Let's discuss this first before adding MISSING_PV to the picture...
FWIW:
raid0 mappings with a subset of missing segments may not be of much use
but will provide data still.
Heinz
I agree with you. the PARTIAL_LV is more closer to the new bit
NOT_USABLE_LV.
There is another bit MISSING_PV, which is set when pv is missing or
the pv is not workable.
From my understanding, we could reuse the PARTIAL_LV to show different
meaning according to different context. For example, in raid env, the
top layer LV will be set PARTIAL_LV when the raid array not usable
(e.g. raid0 missing a disk). Other cases, within raid limit, top layer
raid LV won't be set. if following the rule, there will no need to set
the new bit NOT_USABLE_LV.
Heming
_______________________________________________
linux-lvm mailing list
linux-lvm@xxxxxxxxxx
https://www.redhat.com/mailman/listinfo/linux-lvm
read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
_______________________________________________
linux-lvm mailing list
linux-lvm@xxxxxxxxxx
https://www.redhat.com/mailman/listinfo/linux-lvm
read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
