Centos – How to check 3ware raid controller’s health? (Where to download tw_cli tool?)

No, and if you have 4 disks and want two spares you are better off performance wise with a 4 disk RAID 10 instead of a 3 disk RAID 5 + hot spare. Either way your array will have 2 disks worth of usable capacity but the RAID 10 will have better write speeds and takes less time to recover from a failed disk.

Assuming the RAID 5 doesn't contain your boot volume, I'd go ahead and backup the data, reconfigure to a RAID 10, and restore the data.

    RAID Level Comparison for arrays up to 8 drives.
Features                RAID 0  RAID 1   RAID 5   RAID 6   RAID 10
Min Drives                2       2        3        4        4
Data Protection           0       1        1        2        2 (Up to one disk failure in each sub-array)
Read Performance         High    High     High     High     High
Write Performance        High   Medium    Low      Low     Medium
Degraded Read Perf       N/A    Medium    Low      Low      High
Degraded Write Perf      N/A     High     Low      Low      High
Capacity Utilization %   100     50      67-87    50-75     50

I may have figured it out. I had the opportunity to test it on a spare machine:

I first had this:

# tw_cli /c0 show
Unit  UnitType  Status         %RCmpl  %V/I/M  Stripe  Size(GB)  Cache  AVrfy
------------------------------------------------------------------------------
u0    RAID-5    OK             -       -       256K    5587.9    RiW    ON

VPort Status         Unit Size      Type  Phy Encl-Slot    Model
------------------------------------------------------------------------------
p0    OK             u0   1.82 TB   SATA  0   -            ST32000542AS
p1    OK             u0   1.82 TB   SATA  1   -            ST32000542AS
p2    OK             u0   1.82 TB   SATA  2   -            ST32000542AS
p3    OK             u0   1.82 TB   SATA  3   -            ST32000542AS
p4    OK             -    1.82 TB   SATA  4   -            ST32000542AS

Name  OnlineState  BBUReady  Status    Volt     Temp     Hours  LastCapTest
---------------------------------------------------------------------------
bbu   On           Yes       OK        OK       OK       0      xx-xxx-xxxx

A 4 disk raid 5 and one extra disk.

Then I did this:

# tw_cli /c0/u0 migrate type=raid5 disk=4
Sending migration message to /c0/u0 ... Done.

Then I had this:

# tw_cli /c0/u0 show

Unit     UnitType  Status         %RCmpl  %V/I/M  Port  Stripe  Size(GB)
------------------------------------------------------------------------
u0       Migrator  MIGRATING      -       0%      -     -       -

su0      RAID-5    OK             -       -       -     256K    5587.9
su0-0    DISK      OK             -       -       p0    -       1862.63
su0-1    DISK      OK             -       -       p1    -       1862.63
su0-2    DISK      OK             -       -       p2    -       1862.63
su0-3    DISK      OK             -       -       p3    -       1862.63
su0/v0   Volume    -              -       -       -     -       50
su0/v1   Volume    -              -       -       -     -       5537.9

du0      RAID-5    OK             -       -       -     256K    7450.54
du0-0    DISK      OK             -       -       p0    -       1862.63
du0-1    DISK      OK             -       -       p1    -       1862.63
du0-2    DISK      OK             -       -       p2    -       1862.63
du0-3    DISK      OK             -       -       p3    -       1862.63
du0-4    DISK      OK             -       -       p4    -       1862.63
du0/v0   Volume    -              -       -       -     -       N/A
du0/v1   Volume    -              -       -       -     -       N/A

su0 and du0 are probably source and destination, giving me a new and bigger u0 at the end. I would think that du0/v0 and du0/v1 will become active when the migrating is done. But this is going to take a week to migrate and I don't know if I have the patience for that...