Re: Full use of varying drive sizes?

[Goswin von Brederlow <goswin-v-b@web.de>]

Tapani Tarvainen <raid@tapanitarvainen.fi> writes:

> On Tue, Sep 22, 2009 at 04:07:53PM +0300, Majed B. (majedb@gmail.com) wrote:
>
>> When I first put up a storage box, it was built out of 4x 500GB disks,
>> later on, I expanded to 1TB disks.
>> 
>> What I did was partition the 1TB disks into 2x 500GB partitions, then
>> create 2 RAID arrays: Each array out of partitions:
>> md0: sda1, sdb1, sdc1, ...etc.
>> md1: sda2, sdb2, sdc2, ...etc.
>> 
>> All of those below LVM.
>> 
>> This worked for a while, but when more 1TB disks started making way
>> into the array, performance dropped because the disk had to read from
>> 2 partitions on the same disk, and even worse: When a disk fail, both
>> arrays were affected, and things only got nastier and worse with time.
>
> I'm not 100% sure I understand what you did, but for the record,
> I've got a box with four 1TB disks arranged roughly like this:
>
> md0: sda1, sdb1, sdc1, sde1
> md1: sda2, sdb2, sdc2, sde2
> md2: sda3, sdb3, sdc3, sde3
> md3: sda4, sdb4, sdc4, sde4
>
> and each md a pv under lvm, and it's been running problem-free
> for over a year now. (No claims about performance, haven't
> made any usable measurements, but it's fast enough for what
> it does.)
>
> When it was new I had strange problems of one disk dropping out of the
> arrays every few days. The reason was traced to faulty SATA controller
> (replacing it fixed the problem), but the process revealed an extra
> advantage in the partitioning scheme: the lost disk could be added
> back after reboot and array rebuilt, but the fault had appeared
> in only one md at a time, so recovery was four times faster
> than if the disks had had only one partition.

In such a case bitmaps will bring the resync time down to minutes.

MfG
        Goswin