On 10/7/19 12:31 pm, Reindl Harald wrote:
Am 10.07.19 um 04:18 schrieb Adam Goryachev:
On 10/7/19 11:57 am, Reindl Harald wrote:
Am 10.07.19 um 03:28 schrieb Adam Goryachev:
TBH, I really don't understand RAID10, other than improving performance.
For example, in a 10 drive RAID10, you have a higher probability to lose
2 drives that are a "pair" than losing 3 drives in total from a 7 drive
RAID6 (both events lead to total data loss, although potentially you
could recover more "usable" data from the RAID10 array since you would
more likely have a large amount of contiguous data).
RAID10 is about performance *and* redundancy *as well* as storage size
as said: 3 disk RAID10 is a joke and a 3 disk RAID1 is waste of size
3x2 TB RAID1 = 2 TB useable
4x2 TB RAID10 = 4 TB useable
So for the cost of an extra 2TB drive, you got:
1) An extra 2TB capacity - which the OP doesn't need
2) Less data protection, you can only lose a MAXIMUM of 2 disks without
losing data, but if you lose the "wrong" 2 disks, then you lost all your
data.
Using 4 x 2TB RAID1 (ie, same cost/number of disks) would mean you can
lose any 3 disks with no data loss, and when you replace them, quick and
simple recovery process. Even 3 x 2TB allows for ANY 2 disk failure
without data loss.
The OP stated that performance and capacity was not something that
interests him. The primary concern was avoiding the loss of data,
presumably due to drive failure, perhaps availability is also important.
2TB is sufficient for 5 years.
don't change the fact that a 2 TB HDD (when we say performance is not
important) costs nothing these days and with RAID1 you are limited to
the write speed of a single disk
so if you are paranoid about drive failures get 6x1 TB = 300 € with 3 TB
useable which is exatcly between 3x2 RAID1 and 4x2 RAID10 :-)
Assuming you are now suggesting 6 x 1TB in RAID10 with 2 mirrors (to get
3TB usable) then you are still suffering from the 2 drive failures
causing loss of all data (although potentially you can lose 3 with no
data loss). In fact, you might be better off with RAID6 where you can
lose ANY 2 drives (I haven't had enough coffee to work out probabilities
on these things). Also, the OP advised their system can only support a
maximum of 3 drives.
So, you say if I'm really paranoid about drive failures... but how does
that improve the situation? If I was truly paranoid about drive
failures, and not concerned with capacity, then I'd buy 6 x 2TB drives
in RAID1 with 6 mirrors, allowing for any 5 drive failures with no data
loss. Though I'm not sure anyone would really do that (or be that
paranoid), as you are likely to have "other" hardware failures before
you will have multiple (that many) drive failures before being able to
replace and re-sync the drives. I would be looking at other options like
DRBD to real-time sync to another machine, and have both machines with
RAID1 x 3 or RAID1 x 2 rather than RAID1 x 4 or more.
Regards,
Adam
--
Adam Goryachev Website Managers www.websitemanagers.com.au
--
The information in this e-mail is confidential and may be legally privileged.
It is intended solely for the addressee. Access to this e-mail by anyone else
is unauthorised. If you are not the intended recipient, any disclosure,
copying, distribution or any action taken or omitted to be taken in reliance
on it, is prohibited and may be unlawful. If you have received this message
in error, please notify us immediately. Please also destroy and delete the
message from your computer. Viruses - Any loss/damage incurred by receiving
this email is not the sender's responsibility.
