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Old 07-13-2012, 08:17 PM
"Alan J. Gagne"
 
Default "best practices" for using a small SSD boot drive and a big regular one?

> [agagne at dw-agagne ~]$ df -h
> Filesystem***************************** Size* Used Avail Use% Mounted on
> rootfs********************************** 50G* 7.7G** 40G* 17% /
> devtmpfs******************************* 7.9G**** 0* 7.9G** 0% /dev
> tmpfs********************************** 7.9G* 2.1M* 7.9G** 1% /dev/shm
> tmpfs********************************** 7.9G* 884K* 7.9G** 1% /run
> /dev/mapper/vg_dwagagne01-lv_root******* 50G* 7.7G** 40G* 17% /
> tmpfs********************************** 7.9G**** 0* 7.9G** 0% /sys/fs/cgroup
> tmpfs********************************** 7.9G**** 0* 7.9G** 0% /media
> /dev/sda2****************************** 497M* 114M* 358M* 25% /boot
> /dev/mapper/vg_dwagagne01-lv_home******* 81G** 11G** 67G* 14% /home
> /dev/mapper/vg_dwagagne02-lv_opt******** 50G* 2.0G** 46G** 5% /opt
> /dev/mapper/vg_dwagagne02-lv_vmachines* 250G* 127G* 111G* 54% /vmachines
> /dev/mapper/vg_dwagagne02-lv_scratch*** 200G** 30G* 160G* 16% /scratch

sorry, i'm not sure what's going on up there. first, are you saying
that when you installed, you picked both drives as installable devices
and you just went with with what the installer chose for the first
(SSD) drive?

and i'm assuming that you used your entire 2nd drive for the "02"
volume group, is that it?



Sorry for the lack of clarity.



I installed to the first drive only letting Fedora set-up
partitioning.

The second drive I set-up manually after the os install.

Currently the second drive is using 550GB of the 750 for VG 02.

200GB on the second drive is currently being left in reserve.



Alan



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Old 07-14-2012, 10:56 AM
Reindl Harald
 
Default "best practices" for using a small SSD boot drive and a big regular one?

Am 14.07.2012 12:47, schrieb Roberto Ragusa:
> On 07/14/2012 11:55 AM, Robert P. J. Day wrote:
>> On Sat, 14 Jul 2012, Heinz Diehl wrote:
>>
>>> On 14.07.2012, Joe Zeff wrote:
>>>
>>>> Not swap. If you really need swap, it gets written to over and over, which
>>>> isn't exactly the best thing for an SSD.
>>>
>>> My thoughts were that nowadays, on laptops with a fairly amount of
>>> RAM, swap gets mainly used for hibernating, and I think it will be a
>>> significant advantage to have the memory image recovered from the
>>> fastest disk in the system.
>>
>> oh, right, *that's* why i want swap. :-)
>>
>
> If your rotating disk will always be connected, you may want to have
> a unique VG across both the SSD and the HD, so you can move partitions
> across them and have more flexibility.
> For example, if you realize to need some more space on a SSD filesystem,
> you still have to ability to enlarge the partition into the HD and cope with
> a partially-here/partially-there layout.
> This road can lead to very interesting tricks, such as having the
> journal and metadata on SSD and actual data on HD.

and what happens if ONE drive fails?

colume groups over different drives are a VERY bad idea
as long LVM does not sit on top of a RAID!

having as example a LVM over 3 drives makes it 3 times
more possible to lose the whole volume groups data
if one drive goes down

this is the same as for RAID0: do it only if it does
not bother you losing your data!

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Old 07-16-2012, 03:56 PM
Roberto Ragusa
 
Default "best practices" for using a small SSD boot drive and a big regular one?

On 07/14/2012 12:56 PM, Reindl Harald wrote:
>> If your rotating disk will always be connected, you may want to have
>> a unique VG across both the SSD and the HD, so you can move partitions
>> across them and have more flexibility.
>> For example, if you realize to need some more space on a SSD filesystem,
>> you still have to ability to enlarge the partition into the HD and cope with
>> a partially-here/partially-there layout.
>> This road can lead to very interesting tricks, such as having the
>> journal and metadata on SSD and actual data on HD.
>
> and what happens if ONE drive fails?

Maybe restore from backup?
Backups on Linux are trivial: external drive + rsync/rsnapshot.

Not having a backup is a risk even with only one drive.
HDs fail, SSDs fail, laptop are dropped/lost/stolen.

Protecting your data doesn't imply you have to run away
from RAID-0 in panic.

> colume groups over different drives are a VERY bad idea
> as long LVM does not sit on top of a RAID!
>
> having as example a LVM over 3 drives makes it 3 times
> more possible to lose the whole volume groups data
> if one drive goes down

Yes.
A 500,000 hours MTBF is 114 years of usage (at 12 hours per day).
Three similar drives in RAID-0 is 38 years of usage (at 12h/day).

> this is the same as for RAID0: do it only if it does
> not bother you losing your data!

Don't be so dogmatic.
Just estimate the risk and take countermeasures.

As regards my future SSD+HD project that I cited before, be assured
that I'm using 2 RAID1 SSDs and 8 RAID10 HDs.
Plus rsync backups every 4 hours.
Plus daily remote backup.
But this is a production server. On a laptop you can't do that;
the laptop is so easily damaged/lost that your data should be
backupped anyway just for that; at that point why not play with
some smart disk arrangement to make it work faster?

--
Roberto Ragusa mail at robertoragusa.it


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