data switchs su,sw and sunit,swidth
Resending this as I never saw it show up on the list (sent out yesterday) (while other the messages came back in under 15 minutes or so)...
Have started to use RAID on a few of my disks and forgot about the xfs 'su*sw' and 'sunit*swidth' options.
Quoted 1 line
From what I get in reading the manpage, 'su' is used with 'sw' and
'sunit' is used with 'swidth'?
The RAID controller in one of my machines uses a "strip element" size, expressed in bytes, allowed values seem to be limited to powers of 512*2^*[1..11] (512B up to 1MB) (though as previously noticed, although xfs's manpages claims to allow one expresses sizes with the unit 'm', it
only permits .25m (256k), I guess I never tried seeing if the command line would take floating point ;^) ).
I believe 'su' would be set to the 'strip element size' (in k or m).
Then, for RAID 1 (mirror) would 'sw'==1? Would setting the su/sw value
for a RAID 1 actually matter in any way? Ie, technically -- it would fill in numbers for OS book-keeping, but wouldn't change anything in terms of performance or layout, vs. 'physically' -- where it could change disk layout or performance?
At RAID 0, I'd guess sw==2?
In RAID 5, would it be sw == #Disks-1? So even w/6 disks, it still only
uses 1 disk for parity and sw == 5?
I wonder what becomes a max-safe RAID 5 size? (or is the number of parity disks a settable option with RAID 5?)
Thanks!...
Linda
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Quoted 7 lines · On Sonntag 19 Juli 2009 Linda Walsh wrote:
Then, for RAID 1 (mirror) would 'sw'==1? Would setting the su/sw value for a RAID 1 actually matter in any way? Ie, technically -- it would fill in numbers for OS book-keeping, but wouldn't change anything in terms of performance or layout, vs. 'physically' -- where it could change disk layout or performance?
At RAID 0, I'd guess sw==2?
Both RAID0 and RAID1 use sw=0.
Quoted 2 lines
In RAID 5, would it be sw == #Disks-1? So even w/6 disks, it still only uses 1 disk for parity and sw == 5?
RAID5: sw = #Disks-1 ( so with 8 disks use 7)
RAID6: sw = #Disks-2 ( so with 8 disks use 6)
Quoted 2 lines
I wonder what becomes a max-safe RAID 5 size? (or is the number of parity disks a settable option with RAID 5?)
RAID5 always only has 1 parity disk (well, technically it's not a physical disk, but the parity is distributed over all disks in the array).
Don't know what you mean by "max-safe" size. The more disks you have, the bigger the chance that a single disk breaks. Also, I tested with Areca controllers, using more than 7 disks in a single RAID array doesn't improve speed anymore. So I use RAID-6 for up to 8 disks, and make it RAID-60 for up to 16 disks (with Areca controllers).
mfg zmi
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