Question : Problem: RAID5 with a Hot-spare or RAID10

Hello all:

   I searched through the questions and didn't find one that fit my situation, so here goes.  I'm planning a new server for a client - originally with 5 * 250 GB SATA drives, RAID5 with a hot spare - approx 750 GB usable.  I was then talking with them about the new Seagate 500 GB SATA-II drives with doubled (3.0 Gb) speed which perked my client's interest and he told me to get those.  4 * 500 GB in RAID5 with a hot spare gives 1 TB usable.  But 4 *500 GB in a RAID10 also gives 1 TB.  (This may be a little overkill for this client since they only have about 15 users, no email, no web site on the server, just file and print, Quickbooks, and a dispatch database program that two PCs will use.)  
   This client is in a very remote location, so I'm probably more interested in reliability more than speed, (although my client likes speed as well :).  They had a drive that crashed a few months ago and so has prompted a backup/redundancy movement - hence the server.  I don't think hot spares are available for RAID10, but in choosing between the two, what would be safer???

Thanks,
Jon

Answer : Problem: RAID5 with a Hot-spare or RAID10

"Safer" is a matter of perspective here.   In this case the $$/gb cost is the same => since with either of your plans you're guying 4 hard drives.

In the RAID 10 case you can have any one drive fail -- and if the "right" 2nd drive fails you can sustain that loss as well; but if the "wrong" 2nd drive fails you're in trouble.   Meanwhile, you're (a) running at risk; and (b) continue to run at risk until you are notified, get on site, and replace the failed disk.

In the RAID 5 case you can have any one drive fail -- and if any 2nd drive fails you're in trouble.   But as long as that doesn't happen, the hot spare takes over, and the system is only at risk for the length of the rebuild -- regardless of whether you've been notified or not.

Performance-wise, the RAID 10 will have better write performance, and read performance is essentially the same.

For a relatively remote location, IF you are limited to 4 drives, I'd go with the RAID-5 and hot spare.  HOWEVER, the better RAID controllers (e.g. 3Ware) support hot spares for any array -- so with 5 drives you could build a RAID-10 array with a hot spare.   THAT would be ever better.