Re: [linux-lvm] Is TRIM and DISCARD needed for normal HDD ?

2020-11-26 Thread Marek Podmaka
Title: Re: [linux-lvm] Is TRIM and DISCARD needed for normal HDD ?


Hi,

TRIM is also used on some SMR HDDs.

https://superuser.com/questions/1407990/what-does-trim-on-an-hdd-mean

Wednesday, November 25, 2020, 16:37:07, you wrote:





Hi,

I am using thin LVM pools, but I have a normal hard disk and not a SSD.

Is there any reason to enable TRIM and/or DISCARD for my HDD ?

I have heard it is only useful for a SSD. Will it offer any advantages in my case ?

--
Regards,
Sreyan Chakravarty



                

--
  bYE, Marki

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Re: [linux-lvm] Is TRIM and DISCARD needed for normal HDD ?

2020-11-26 Thread Zdenek Kabelac

Dne 25. 11. 20 v 16:37 Sreyan Chakravarty napsal(a):

Hi,

I am using thin LVM pools, but I have a normal hard disk and not a SSD.

Is there any reason to enable TRIM and/or DISCARD for my HDD ?

I have heard it is only useful for a SSD. Will it offer any advantages in my 
case ?




Hi

Thin-pool is created by default with 'passdown' TRIM/discard support.

This means - discard to thin LV  (i.e. fstrim of ext4 on thinLV) gets 
propagated to thin-pool, where it may deallocate full chunk when possible 
(i.e. if you use  256K chunk, WHOLE chunk must be free to have an effective 
discard).


With "passdown" mode - such released chunks are also then passed through to 
origin _tdata device - where again some 'alignment rules' of discardable 
regions applie (i.e. lot of SSD need 512KiB blocks).


If you have HDD - then clearly such discard stops at thin-pool level 
(automatically) and just releases chunks in thin-pool for future reuse.


"ignore" discard mode is usefull in the case you want to keep already 
'allocated' chunks for thin LV always there - and also in some case it may 
make timing more predictible - as discard requires processing - so it ma 
slowdown few things - but at the expense of more filled thin-pool


Hopefully this makes it clear.

Regards

Zdenek

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[linux-lvm] Is TRIM and DISCARD needed for normal HDD ?

2020-11-26 Thread Sreyan Chakravarty
Hi,

I am using thin LVM pools, but I have a normal hard disk and not a SSD.

Is there any reason to enable TRIM and/or DISCARD for my HDD ?

I have heard it is only useful for a SSD. Will it offer any advantages in
my case ?

-- 
Regards,
Sreyan Chakravarty
___
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linux-lvm@redhat.com
https://www.redhat.com/mailman/listinfo/linux-lvm
read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/