Different between "iostat 5" and "zpool iostat 5"

Question

Hi,
if using ZFS, is it recommended to use zpool iostat over the normal iostat?
Basically what is the different between both?
In normal iostat, what is the most valuable info we need to look into to measure the performance? a_svc, b%, w%?
where in zpool iostat, what is the most valuable info we need to look into to measure the performance? and how to determine it is slow or fast? since, there are no a_svc, b%, w%??
in the following info in http://docs.oracle.com/cd/E19253-01/819-5461/gammt/index.html?
# zpool iostat
capacity operations bandwidth
pool alloc free read write read write
rpool 6.05G 61.9G 0 0 786 107
tank 31.3G 36.7G 4 1 296K 86.1K
what does 786 and 107 for rpool refer to? kilobyte?bytes? bit?
Thanks

Answer 1

if using ZFS, is it recommended to use zpool iostat over the normal iostat?I like both of them, but I'd recommend 'zpool iostat -v' because it will also give you per-device statistics through zpool.
Basically what is the different between both?iostat displays statistics for all devices, zpool iostat will only give statistics for devices in a zpool. When you have cache and log devices and mirrors and stuff configured, iostat may not be very easy to read. But iostat has information on service time that zpool iostat does not have
In normal iostat, what is the most valuable info we need to look into to measure the performance? a_svc, b%, w%?I usually look at number of operations (read and write), service time (svc_t) and sometimes the throughbut (kread, kwrite). I don't trust %b or %w because I nerver really understood how they are calculated, I also suspect they may be calculated differently on different platforms (linux and solaris) and I have seen cases where they have just been wrong. So I go by rules of thumb for operations and service times:
A single disk should be able to provide ~100 random read operations per second. Maybe 150, maybe 75 but definitely somewhere in that region. If the reported number gets close to that (or bigger), I start to get worried.
The service time of a random read request should be about 4-6ms. Maybe 7 or 8. But if the service time is reported in double-digits, I start to get worried.
Everything else will depend on your application and your threshold for nervousness. Some of my customers feel ok until %b reaches 80%, some may think that service times of 12ms are ok. The best way is to compare these numbers to baselines from when the system is performing OK.
where in zpool iostat, what is the most valuable info we need to look into to measure the performance? and how to determine it is slow or fast? since, there are no a_svc, b%, w%??again, reads and writes is usually what I look for.
in the following info in http://docs.oracle.com/cd/E19253-01/819-5461/gammt/index.html?
# zpool iostat
capacity operations bandwidth
pool alloc free read write read write
rpool 6.05G 61.9G 0 0 786 107
tank 31.3G 36.7G 4 1 296K 86.1K
what does 786 and 107 for rpool refer to? kilobyte?bytes? bit?bandwidth is reported in bytes. In this case, zpool iostat was called without a repeat-interval so only the average since system boot is reported. So in this case 786 bytes have been read per second on average since system start. Quite a useless number.
Bjoern