Hi Marian,
1. As there are more disks in the VG, can them all work with larger
max_sectors_kb?
All four disks and relative MD device has max_sectors_kb set to the
required (large) 2048 value.
They all are recent (circa 2010) SATA disks, albeit from different
vendors.
2. Does it work for md device without stacking LVM on top of that?
I did not try to directly use the MD device. Let me test this and I will
report here.
3. What's your Physical extent size?
vgs -ovg_extent_size vg_kvm # or simple vgs -v
PE size is at default (4MiB).
4. If all above is fine then it may be related to LVM.
I think so, because I did some test with a _single_ disk (an SSD,
actually) with and without LVM on top. Without LVM, I see the normal and
expected behavior - IO transfer size increase with max_sectors_kb. With
LVM on top, I see the exact same behavior I am reporting: max IO
transfer size seems capped at 512 KB, regardless the max_sectors_kb
setting.
It really seems something related to LVM layer.
-- Marian
Thanks.
--
Danti Gionatan
Supporto Tecnico
Assyoma S.r.l. - www.assyoma.it
email: g.danti@assyoma.it - info@assyoma.it
GPG public key ID: FF5F32A8
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