[linux-lvm] stripped LV with segments vs one segment

Discussion:

lejeczek

2017-04-10 09:29:13 UTC

hi there

I could not extend my stripped LV, had 3 stripes and wanted
to add one more.
Only way LVM let me do it was where I ended up with this:

--- Segments ---
Logical extents 0 to 751169:
Type striped
Stripes 3
Stripe size 16.00 KiB
Stripe 0:
Physical volume /dev/sdd
Physical extents 0 to 250389
Stripe 1:
Physical volume /dev/sde
Physical extents 0 to 250389
Stripe 2:
Physical volume /dev/sdc
Physical extents 0 to 250389

Logical extents 751170 to 1001559:
Type linear
Physical volume /dev/sdf
Physical extents 0 to 250389

1st question - was this really the only way LVM would extend?
2nd - is there performance penalty with segments like above
vs one stripped segment?

many thanks,
L.

Zdenek Kabelac

2017-04-10 11:03:39 UTC

Permalink

Post by lejeczek
hi there
I could not extend my stripped LV, had 3 stripes and wanted to add one more.
--- Segments ---
Type striped
Stripes 3
Stripe size 16.00 KiB
Physical volume /dev/sdd
Physical extents 0 to 250389
Physical volume /dev/sde
Physical extents 0 to 250389
Physical volume /dev/sdc
Physical extents 0 to 250389
Type linear
Physical volume /dev/sdf
Physical extents 0 to 250389
1st question - was this really the only way LVM would extend?
2nd - is there performance penalty with segments like above vs one stripped
segment?

Hi

Not really sure what you aim to do.

If you have LV segment with 3 stripes - you have to keep also extension using
3 stripes - you can't have 1st. halve of LV spanning 3 disk and add there a
new LV segment as linear - as listed in this post.

Both segments must by striped.

Regards

Zdenek

lejeczek

2017-04-10 11:16:18 UTC

Permalink

Post by Zdenek Kabelac

Post by lejeczek
hi there
I could not extend my stripped LV, had 3 stripes and
wanted to add one more.
--- Segments ---
Type striped
Stripes 3
Stripe size 16.00 KiB
Physical volume /dev/sdd
Physical extents 0 to 250389
Physical volume /dev/sde
Physical extents 0 to 250389
Physical volume /dev/sdc
Physical extents 0 to 250389
Type linear
Physical volume /dev/sdf
Physical extents 0 to 250389
1st question - was this really the only way LVM would
extend?
2nd - is there performance penalty with segments like
above vs one stripped
segment?

Hi
Not really sure what you aim to do.
If you have LV segment with 3 stripes - you have to keep
also extension using 3 stripes - you can't have 1st.
halve of LV spanning 3 disk and add there a new LV segment
as linear - as listed in this post.
Both segments must by striped.
Regards
Zdenek

I had 3 stripe LV, you know, three PVs, and wanted the LV to
have 4 stripes, wanted to add 4th PV, you can see it from
above lvdisplay.
I tried these and each time it errored:
$ lvextend -v -i 4 -l+100%free dellH200.InternalB/0
$ lvextend -v -i 4 -l+100%pv dellH200.InternalB/0 /dev/sdf
$ lvextend -i 4 -l 100%vg dellH200.InternalB/0

I did have only one segment, an LV spanning 100%vg with
100%each-pv.
And the above is the result of: $ lvextend -i 1 -l +100%free
dellH200.InternalB/0 /dev/sdf

so, either I'm not getting it right or a stripped LV cannot
be extended this way - then: is there performance penalty
with segments like above vs one stripped
segment?

Marian Csontos

2017-04-10 12:27:19 UTC

Permalink

I had 3 stripe LV, you know, three PVs, and wanted the LV to have 4
stripes, wanted to add 4th PV, you can see it from above lvdisplay.

What you want is "reshape" not extend. This was committed as RAID
feature to 2.02.169, but it is still somewhat experimental. You would
need to convert stripe LV to RAID0 (aka takeover) and then reshape.

$ lvextend -v -i 4 -l+100%free dellH200.InternalB/0
$ lvextend -v -i 4 -l+100%pv dellH200.InternalB/0 /dev/sdf
$ lvextend -i 4 -l 100%vg dellH200.InternalB/0

lvextend With -i 4 this would add another striped segment with 4 devices
after the first segment - and IIUC you do not have enough space for that.

I did have only one segment, an LV spanning 100%vg with 100%each-pv.
And the above is the result of: $ lvextend -i 1 -l +100%free
dellH200.InternalB/0 /dev/sdf
so, either I'm not getting it right or a stripped LV cannot be extended
this way - then: is there performance penalty with segments like above
vs one stripped
segment?
_______________________________________________
linux-lvm mailing list
https://www.redhat.com/mailman/listinfo/linux-lvm
read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/

lejeczek

2017-04-10 13:35:24 UTC

Permalink

Post by Marian Csontos

Post by lejeczek
I had 3 stripe LV, you know, three PVs, and wanted the LV
to have 4
stripes, wanted to add 4th PV, you can see it from above
lvdisplay.

What you want is "reshape" not extend. This was committed
as RAID feature to 2.02.169, but it is still somewhat
experimental. You would need to convert stripe LV to RAID0
(aka takeover) and then reshape.

thanks, I see it more clearly now.
Is it possible to get rid of that second segment now? Have
the LV prior to extension?

Post by Marian Csontos

Post by lejeczek
$ lvextend -v -i 4 -l+100%free dellH200.InternalB/0
$ lvextend -v -i 4 -l+100%pv dellH200.InternalB/0 /dev/sdf
$ lvextend -i 4 -l 100%vg dellH200.InternalB/0

lvextend With -i 4 this would add another striped segment
with 4 devices after the first segment - and IIUC you do
not have enough space for that.

Post by lejeczek
I did have only one segment, an LV spanning 100%vg with
100%each-pv.
And the above is the result of: $ lvextend -i 1 -l +100%free
dellH200.InternalB/0 /dev/sdf
so, either I'm not getting it right or a stripped LV
cannot be extended
this way - then: is there performance penalty with
segments like above
vs one stripped
segment?
_______________________________________________
linux-lvm mailing list
https://www.redhat.com/mailman/listinfo/linux-lvm
read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/

_______________________________________________
linux-lvm mailing list
https://www.redhat.com/mailman/listinfo/linux-lvm
read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/

Marian Csontos

2017-04-11 17:16:01 UTC

Permalink

Post by lejeczek

Post by Marian Csontos

I had 3 stripe LV, you know, three PVs, and wanted the LV to have 4
stripes, wanted to add 4th PV, you can see it from above lvdisplay.

thanks, I see it more clearly now.
Is it possible to get rid of that second segment now? Have the LV prior
to extension?

Either lvresize to previous size or vgcfgrestore would work UNLESS you
resized the filesystem as well. vgcfgrestore has more limitations - no
other metadata altering operations were performed on VG since the change.

Marian

lejeczek

2017-04-10 14:27:49 UTC

Permalink

Post by Marian Csontos

Post by lejeczek
I had 3 stripe LV, you know, three PVs, and wanted the LV
to have 4
stripes, wanted to add 4th PV, you can see it from above
lvdisplay.

What you want is "reshape" not extend. This was committed
as RAID feature to 2.02.169, but it is still somewhat
experimental. You would need to convert stripe LV to RAID0
(aka takeover) and then reshape.

convert from stipe to raid0 would not preserve stripe sizes?
is this correct?
nor it would:

-I/--stripesize not allowed for LV dellH200.InternalB/0 when
converting from striped to raid0.

LVM version: 2.02.166(2)-RHEL7 (2016-11-16)
Library version: 1.02.135-RHEL7 (2016-11-16)
Driver version: 4.35.0

Post by Marian Csontos

Post by lejeczek
$ lvextend -v -i 4 -l+100%free dellH200.InternalB/0
$ lvextend -v -i 4 -l+100%pv dellH200.InternalB/0 /dev/sdf
$ lvextend -i 4 -l 100%vg dellH200.InternalB/0

lvextend With -i 4 this would add another striped segment
with 4 devices after the first segment - and IIUC you do
not have enough space for that.

Marian Csontos

2017-04-11 17:37:36 UTC

Permalink

Post by Marian Csontos

I had 3 stripe LV, you know, three PVs, and wanted the LV to have 4
stripes, wanted to add 4th PV, you can see it from above lvdisplay.

convert from stipe to raid0 would not preserve stripe sizes? is this
correct?

It should keep stripe size and if it does not it is a bug.

-I/--stripesize not allowed for LV dellH200.InternalB/0 when converting
from striped to raid0.

As it says, the option is simply not allowed. Also it would be
meaningless - one can not change stripe size while converting stripe to
raid0. At least not in RHEL-7.3 (lvm2-2.02.166). This is supposed to
work in upstream/2.02.169, but keep in mind that is a new feature, and
it is altering data, so better keep a working backup.

LVM version: 2.02.166(2)-RHEL7 (2016-11-16)
Library version: 1.02.135-RHEL7 (2016-11-16)
Driver version: 4.35.0

lejeczek

2017-04-11 18:26:02 UTC

Permalink

Post by Marian Csontos

Post by lejeczek

Post by Marian Csontos

Post by lejeczek
I had 3 stripe LV, you know, three PVs, and wanted the
LV to have 4
stripes, wanted to add 4th PV, you can see it from
above lvdisplay.

What you want is "reshape" not extend. This was
committed as RAID
feature to 2.02.169, but it is still somewhat
experimental. You would
need to convert stripe LV to RAID0 (aka takeover) and
then reshape.

convert from stipe to raid0 would not preserve stripe
sizes? is this
correct?

It should keep stripe size and if it does not it is a bug.

then probably a bug, I don't have it as was on the console
in front of me now, but should be easy to replicate.
I had stripe LV with 16KB stripe and conversion(successful)
to raid0 said I got 64KB stripe raid0 - is how I remember it.

Post by Marian Csontos

Post by lejeczek
-I/--stripesize not allowed for LV dellH200.InternalB/0
when converting
from striped to raid0.

As it says, the option is simply not allowed. Also it
would be meaningless - one can not change stripe size
while converting stripe to raid0. At least not in RHEL-7.3
(lvm2-2.02.166). This is supposed to work in
upstream/2.02.169, but keep in mind that is a new feature,
and it is altering data, so better keep a working backup.

Post by lejeczek
LVM version: 2.02.166(2)-RHEL7 (2016-11-16)
Library version: 1.02.135-RHEL7 (2016-11-16)
Driver version: 4.35.0

Zdenek Kabelac

2017-04-10 14:19:40 UTC

Permalink

Post by Zdenek Kabelac

Hi
Not really sure what you aim to do.
If you have LV segment with 3 stripes - you have to keep also extension
using 3 stripes - you can't have 1st. halve of LV spanning 3 disk and add
there a new LV segment as linear - as listed in this post.
Both segments must by striped.
Regards
Zdenek

I had 3 stripe LV, you know, three PVs, and wanted the LV to have 4 stripes,
wanted to add 4th PV, you can see it from above lvdisplay.
$ lvextend -v -i 4 -l+100%free dellH200.InternalB/0
$ lvextend -v -i 4 -l+100%pv dellH200.InternalB/0 /dev/sdf

You can't request stripe 4 (needs 4 disks) and pass just single /dev/sdf
device.

Zdenek