This is to be expected in principal but _not_ in this order of magnitude.
Did you allcoate the original and the snapshot logical volumes on the
same physical device?
If so, this means that you trash different areas of that device
with additional read+write ios per write to the original LV.
Change this to see better performanace.
FYI: LVM1 deals with snapshots in a synchronous way which can be outperformed
by LVM2s asynchronous design.
Regards,
Heinz -- The LVM Guy --
On Thu, Jan 30, 2003 at 12:30:32AM +0900, tester7 A. wrote:
>
> Kernel: 2.4.20
> LVM: 1.0.6 with kernel patched(VFS-lock and lvm-1.0.6)
> CPU: PIII 1.4
> RAM: 512M
>
> This is the output from bonnie++ with lv only and with lv + snapshot
>
> Version 1.03 ------Sequential Output------ --Sequential Input-
> --Random-
> -Per Chr- --Block-- -Rewrite- -Per Chr- --Block--
> --Seeks--
> Machine Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP /sec
> %CP
> lv_wo_snap 2G 78505 32 41745 27 151742 41 435.4 1
> lv_wo_snap 2G 75501 31 40277 25 150466 42 436.8 1
> lv_wo_snap 2G 73933 29 41213 26 150052 41 433.4 1
> lv_wo_snap 2G 76434 30 40980 26 147544 41 399.0 0
> lv_with_sn 2G 1367 0 10196 6 128362 35 437.4 1
> ------Sequential Create------ --------Random
> Create--------
> -Create-- --Read--- -Delete-- -Create-- --Read---
> -Delete--
> files:max:min /sec %CP /sec %CP /sec %CP /sec %CP /sec %CP /sec
> %CP
> lv_wo_snap 16 1669 17 +++++ +++ 2532 23 1464 17 +++++ +++ 475 5
> lv_wo_snap 16 1572 17 +++++ +++ 2265 24 1431 14 +++++ +++ 457 5
> lv_wo_snap 16 1481 17 +++++ +++ 2100 22 1405 15 +++++ +++ 478 6
> lv_wo_snap 16 1536 16 +++++ +++ 2286 23 1513 17 +++++ +++ 458 5
> lv_with_sn 16 625 8 +++++ +++ 2333 26 1174 12 +++++ +++ 460 5
>
>
> After making snapshots for a LV, the write performance goes down from 75M/s
> to 1.3M/s.
>
> Something must be wrong in LVM.
>
>
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*** Software bugs are stupid.
Nevertheless it needs not so stupid people to solve them ***
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
Heinz Mauelshagen Sistina Software Inc.
Senior Consultant/Developer Am Sonnenhang 11
56242 Marienrachdorf
Germany
Mauelshagen@Sistina.com +49 2626 141200
FAX 924446
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